I'm looking at my web hosting arrangements currently pondering whether or not to move my websites to new server arrangements. The main attribute I'm considering is the download speed of retrieving pages from the website. My Drupal websites are the test bed. I'd written an article some time ago about website usability and performance metrics going over known considerations. Essentially if a page takes too long to load, users will be turned off by the site and leave. Studies have shown there is an 8 second window of time where an new visitor makes an initial judgment of a website and whether to stay or leave. The more quickly the page loads the better that first impression is, and the more of that 8 seconds you have to impress them with your pristine content.
I have three sources of data. Firebug can measure download time letting you view for yourself the download speed in your browser on your network connection. The Google Sitemaps service also records page download times and reports a graph in the crawl statistics section. Finally the http://mon.itor.us service can report page download times as well.
Historically I've observed these average download times: VPS server from Rimuhosting 1-1.5 secs, Dreamhost account 2.5+ secs, Advanced account at pair.com 3 secs (or more). That is for Drupal websites, the sites which have static HTML pages download much faster at around 1/4 sec. Those numbers are from the Sitemaps crawl statistics.
As a test I moved one of my sites to A2 Hosting and using mon.itor.us got the following results: (drupal 5, A2): avg=849ms min=329ms max=5697ms
The performance is good except when it's bad.
This graph is for the same website from Google Sitemaps crawl statistics. Note in mid-January that the line dropped downward than before. That lines up perfectly with the move of that website over to A2 Hosting. And of course that the line is lower means less time to download pages and a website that feels faster.
That's good enough to be very attractive and I almost am sold on their service. But.. I came across a couple usability issues with their service (specifically their VPS setup is very obtusely confusing). Meaning I'm still looking.