I run a site called the Daily Paul at www.dailypaul.com. It is Drupal 5.1, hosted with Dreamhost. I've been with them for 3 years - always very happy, until earlier this month, when Dreamhost had a spate of downtime. The site was on a shared server, running beautifully - one day (the day of the Iowa Straw Poll), the site handled 24,000 visitors / 50,000+ page views -- on a shared server, without a hitch! It was beautiful!
But after the generalized problems that Dreamhost had (they got hacked, and then their network went down several times), I switched to their new "Private Server" hoping that would solve the problem http://www.dreamhostps.com/
Initially, the site seemed fine - running lickety split - lightening fast. Then I noticed things were back to like before. Today, was the slowest day ever. It was taking me anywhere from 10 - 30 seconds to load pages - any pages. My hosting provider said that everything is fine - loading up fast, no problem. Likewise, host-tracker.com says the pages are loading up in 1-2 seconds:
http://host-tracker.com/check_res_ajx/503065-0/share/