I agree performance is what matters.
Most of my sites are PHP/MySQL driven and I'm tending toward the idea that the MySQL server is the weak link. I have one site that is capable of .5s page render times (for a few days I was getting them) but many times drifts off into 2-5 second render times, with lovely periods (like right now) of 8-16 second render times. Meanwhile, static sites on the same server are quite snappy. 'Flipper' is my most problematic server - my database on it is not even busy. My forum is apparently on 'Krakatoa' these days and while somewhat busy, is never snappy any more, and varies in response time from passable to painful.
In both cases, the speed doesn't seem to correlate to the activity on my sites. My most painful site (on flipper) is an organizational site that is very lightly used and I'm often the only one it (adding reference documents, tinkering with archives, etc.).