Everything2 is an evolving environment. It's very popular, in that visitors are likely to stick around for more than three or four pages. Besides that, it's extremely themable. Each user can change the look of the site, with lots of different permutations.

EDC has been working on better caching and some runtime code generation tricks to reduce the speed hit. The newest version of the code is much speedier, in my testing.

Besides that, sometimes the network connection goes a little crazy. (You've seen Slashdot stop responding occasionally? It's the same sort of thing.)

For what it's worth, Perl Monks runs on roughly the same software. (I dare say something similar with IIS and ASP will likely be half as fast, unless they've improved database pooling since I last looked into it.)