I remember attending a Drupal7 release party several months ago, 11 months ago actually. It was an exciting time, all this new stuff had gotten into core. I was hoping and looking forward to using the new functionality. But then I started evaluating the status of the contributed modules and realized it wasn't going to be possible. The main blocker at that time was that Views was in a massive rewrite mode leading to Views3, and that this was causing attendant delays in other modules who were depending on Views. Winter turned into spring, spring became summer, summer became fall, and it's almost winter again. I've checked several times in the nigh-on a year since the D7 release party, and todays check was the closest I'd come to being able to do the upgrade.
The following is an inventory of upgrade readiness on one of my sites. I didn't record any status on modules which already have been ported to D7.
The status looks pretty good though the length of this report indicates either that I have too many modules installed, or ...? Many of the modules listed below are either in beta (which makes me reluctant, but I'd probably go ahead and give them a whirl) or else are secondary functionality that doesn't have to be upgraded right now.
But there are a few essential modules that aren't ready. The sticky point for me is the embedded media field module and the flash player integration modules. There's not enough information on the project pages to tell me whether there will be an upgrade path from embedded media field to the new media module. I have thousands of nodes using data in embedded media field and need an upgrade path.
I'm really and truly bummed out that the troll module is abandoned. I use the heck out of that module on another site.
Will I upgrade now? It seems to me wisest to again wait a couple more months.
http://drupal.org/project/abuse - This module is useful to help keep the spammers at bay. There is no 7.x version, but a piece of red text at the top of the page says that active development is going on in the 2.x branch. There is no indication of a 7.x version being developed.
http://drupal.org/project/addthis - This module is one of the necessary paths to enabling your readers to help share your content. It's only viable 7.x version is 7.x-2.1-beta1, hence as a beta version I'm reluctant to use it. The page says that active development is going on in 7.x-4.x-dev but that version is not ready to be used. Hence we're stuck between a beta version and a do-not-use version. Sigh.
http://drupal.org/project/admin - Provides the admin menu that some people are fond of. I personally am a little irritated at it. There is no proper 7.x module, it's still in beta, but the beta version is marked with a green color which implies it's safe for use.
http://drupal.org/project/adsense - This module is a useful way to earn some money. However you can always include adsense advertising by creating a normal block and plopping the HTML into the block, rather than using the adsense module. In any case the only 7.x module is a -dev version whose last modification was several months ago. This doesn't give me confidence we'll ever see a stable 7.x adsense module. I may just have to convert to using straight up blocks to show adsense ads.
http://drupal.org/project/badbehavior - This is another module that's supposed to help keep spammers at bay. There is no 7.x version, and no indication there ever will be one.
http://drupal.org/project/boost - This is a performance boosting module that's highly recommended. The current 7.x is a -dev version whose last modification was in April, which doesn't give me confidence that it's being maintained. Especially as the status says "seeking co-maintainers".
http://drupal.org/project/cache_browser - This module helps you understand the caching system. Since it doesn't provide any end-user-benefit this is an optional module I could ditch during a D7 upgrade. Especially since there is no D7 version and no indication there ever will be one.
http://drupal.org/project/cacherouter - Another module for caching tweaks and performance boosts. It clearly says there will never be a D7 version of this module, and that the various engines will be moved off into other modules. The notes on this page tell me that after a D7 upgrade I'll have to revisit performance boosting and cache configuration.
http://drupal.org/project/captcha - Another module that helps keep spammers at bay. The 7.x module is in beta1 which as I've said above makes me reluctant to use it in production. Good news is the last release date was a couple days ago, which gives me confidence someone is working on this.
http://drupal.org/project/captcha_pack - This on the other hand is in alpha and is marked as seeking co-maintainers.
http://drupal.org/project/checkall - A nice UI tweak to help with checking all the buttons in a form. There's no indication of a 7.x version being developed, and no indication that this feature is moot for D7.
http://drupal.org/project/contentanalysis - This module is an essential aid for SEO manipulation. The 7.x version is in alpha, which makes me very nervous. The functionality is somewhat optional however meaning an D7 upgrade could be done without this module, and then later when it gets out of alpha/beta upgrade it then.
http://drupal.org/project/cck - COMPLEXITY. As we all know, Fields are in Core, hurrah. But it means all the old CCK data has to be migrated. Fortunately there's a HOWTO on this on drupal.org and linked from the CCK project page.
http://drupal.org/project/adsense_injector - A useful thingy for injecting advertising into the middle of a node display. This is being renamed to "Content Injector" and it's functionality is being generalized. That's probably a good thing. The 7.x version is in -dev, which makes me reluctant to use on a live site. The D7 roadmap looks useful. It's an interesting question to wait on a D7 migration to have this module, or not.
http://drupal.org/project/contentoptimizer - Works with Content Analysis on your SEO stuff. It too is in alpha.
http://drupal.org/project/contemplate - Looks like we'll have to ditch this module for D7 and use other means to style node display.
http://drupal.org/project/context - I installed this as a bit of an experiment and am not certain I'm actually using it right now. In any case its 7.x is in beta3.
http://drupal.org/project/date - Its project page says 7.x-2.x is the recommended branch, but that branch is in alpha. Uh.. maybe someone isn't clear on what alpha means, but alpha versions are not supposed to be recommended for production use. Which is it, please?
http://drupal.org/project/email_verify - Helps screen new user registrations to stop spammers. Supposedly. I've seen instances of it stopping legit email addresses. In any case there's no 7.x version, and no indication of when/if/ever.
http://drupal.org/project/emfield - Embedded media field is a useful module for dealing with embedding content from youtube and the like. There is no D7 version, and I know from past reading that the powers that be are abandoning this module in favor of the Media module. BUT the emfield project page doesn't say this. If I were to go by that page alone I'd be feeling rather frustrated because there appears to be no way forward and I have thousands of nodes on several sites that are using this module. The http://drupal.org/project/media project page doesn't give any indication of an upgrade path from emfield. This puts me in an uncomfortable position of not having any clue whether I'll be able to convert the data stored with emfield in those thousands of nodes, into something that can be played on D7.
http://drupal.org/project/fb_social - Essential support for facebook widgets. The 7.x version is in beta2 which, as I've said above, makes me a bit reluctant.
http://drupal.org/project/fasttoggle - A useful UI tweak to help content moderators quickly flip UNPUBLISH on things. The 7.x beta went out a few months ago, it might be okay, who knows.
http://drupal.org/project/features - A useful module for creating modules based on capturing settings or views configurations. I have a couple features modules I'm using in D6. The project page implies to me that the features developed in D6 might not be convertible to features for D7. Hence it's likely I'll have to re-develop re-create my features modules for D7?
http://drupal.org/project/feedburner - Essential for integrating feedburner support on a site. There's no D7 version and the maintainer status is unknown. Uhhh...
http://drupal.org/project/feedbuttons - Useful for helping your readers subscribe to your feed. No D7 version, and like the feedburner module the last update was years ago.
http://drupal.org/project/filefield - NOT NEEDED - Install the CCK content migration module, and move your file fields to fields
http://drupal.org/project/flvmediaplayer - A helper for providing a media player. Because of the great migration to the media module it's unclear to me how this modules function will be handled in D7. This module was installed in support of emfield.
http://drupal.org/project/format_number - This module was installed to support the cache browser module, so it might not be necessary on a D7 system anyway. The function it provides is, well, formatting numbers. There's no indication of a D7 module.
http://drupal.org/project/google_cse - Integrates use of the Google Custom Search Engine service to replace core search, ..etc.. No indication of a D7 version.
http://drupal.org/project/insert_view - A filter that lets you bring a view into a node display. The D7 version is in -dev, and had its last update in February. Not giving me any confidence.
http://drupal.org/project/interwiki - A filter that is supposed to make it easier to link to foreign sites. I'm not entirely sure I'm using it, or maybe I'm using it for some of my amazon links. In any case the 7.x version is in beta2 which generally makes me reluctant. But in this case it might be okay. Dunno
http://drupal.org/project/job_scheduler - Some kinda API for scheduling tasks, that is a service module used by other modules. It's 7.x is in alpha.
http://drupal.org/project/jquery_ui - Brings in some jQuery UI library. I must have installed it to satisfy a requirement from some other module. There's no indication of a 7.x version.
http://drupal.org/project/kwresearch - More SEO stuff. Like the other SEO modules this is in alpha
http://drupal.org/project/linkchecker - Checks if you have broken links on your site. No D7 module in sight
http://drupal.org/project/media_audio_flotsam - There's a slew of Media modules that were part of the emfield cluster, which aren't..uh.. I have no idea really if they're being worked on for the new Media module or what to do.
http://drupal.org/project/messaging - A subsystem for the users to send messages or something or other. It's in 7.x alpha. http://drupal.org/project/notifications is a companion module and it too is in alpha
http://drupal.org/project/nodewords - Provides support for meta tags and other meta thingies in nodes. There will not be a D7 version, instead they're doing a ground up rewrite as the metatag module. There is currently no upgrade path from nodewords to metatag D7. Sigh.
http://drupal.org/project/nofollowlist - A useful but abandoned module that adds rel=nofollow attributes to outgoing links on given domains. There was work going on this year in the D6 branch but the project page says it's abandoned.
http://drupal.org/project/oauth - does something with the OAuth protocol. I think this module is a requirement to use the twitter module and perhaps some others. The project page makes it look like the D7 version isn't ready for use yet.
http://drupal.org/project/opensearchplugin - A useful module to help integrate search of your site into the search bar in a browser. There doesn't seem to be a D7 version in anybody's plans.
http://drupal.org/project/panels - An alternate page layout system for running inside Drupal. The D7 is in Alpha.
http://drupal.org/project/panels_tabs - Tweaking to panels to enable them to display tabs. The D7 is in -dev, not even alpha
http://drupal.org/project/path_redirect - Useful module for issuing redirects on given URL's. This module has been redirected itself to become the http://drupal.org/project/redirect module, which is currently in beta.
http://drupal.org/project/prepopulate - If you want to create a bookmarklet for your site, prepopulate is required to get values out of the bookmarklet URL into form fields. A D7 -dev version is in development but I'm not getting confidence that development is in progress.
http://drupal.org/project/comment_subject - Tweaks to auto-generate comment subjects. The D7 is in alpha, but is marked in a green color indicating it's the recommended version, but if so why is it in alpha?
http://drupal.org/project/readability - Another module in the SEO cluster that gives you readability scoring. This one is in D7 beta.
http://drupal.org/project/simplenews - A newsletter service so you can run a mailing list out of your site. The D7 version is in alpha and in active development.
http://drupal.org/project/spamspan - Obfuscates email addresses published on on a Drupal site to foil spammers. The D7 is in beta.
http://drupal.org/project/swftools - Helper for embedding flash players etc. The project page says that "D7 development is back on" but there's no indication of a time frame.
http://drupal.org/project/tableofcontents - Turns H tags to a nice table of contents block. D7 is in -dev.
http://drupal.org/project/taxonomy_breadcrumb - Nice breadcrumb support based on taxonomy. D7 is in -dev but I'm not confident it's being worked on.
http://drupal.org/project/taxonomy_manager - Way useful for managing taxonomy. D7 is in beta.
http://drupal.org/project/troll - Extremely useful to aid content moderators in dealing with spammers. Unfortunately this module is abandoned.
http://drupal.org/project/user_register_notify - Useful for screening new user registrations so you can get a heads-up on spammers. D7 version is in alpha (maybe beta) and the project page implies it's okay.
http://drupal.org/project/username_check - Helps new registrants pick a name. D7 is in -dev