Full credit to MacOS Rumors, they reported that installing the Developer Tools (the third CD in the OS X retail box) made everything faster. I just tried it, and it's definitely true--even IE is zippier.
[Editor's Note: I've read this in a few places, but can't help confirm any speedup. I installed the Dev Tools about three minutes after I installed OS X, so they were in place when I ran my benchmarks. The theory that I've seen elsewhere on the net is that the "Optimizing System" step that happens at the end of the Dev Tools install was supposed to also happen at the end of the OS X install, but a bug stops it from running.
I'm not sure whether I believe it or not, but if you have the free disk space (600mb or so), it can't hurt to try. If you do, though, please time some application launches before and after you install the Dev Tools, and report back with your results. It'd be nice to have some objective evidence to back this theory!]
NOTE: You can run the "optimizing" routine at any time, by starting a terminal and entering:
sudo update_prebinding -root /
This can take quite a while to run, and may (or may not) speed up application launching times. G3-based users have reported speedups; most G4 owners have not seen any changes. Use at your own risk, and you may or may not see any benefit.

