OKCupid is the only web site I can think of that has a regular, not occasional, pattern of being very slow and simply not responding to an unusual number of requests. Hitting F5 to reload a page just to get it to show up instead of the Firefox server unavailable message is a regular part of my usage of the site.
Even though all sites have bugs, broken links, what have you, I don't know any other site that's given me such an expectation that it will be unresponsive for a significant number of page views for any given session over a long term period. Even the sites that started development circa 2003.