[curiousuburb]

I went hunting and cleaning one day (primarily to reclaim drivespace, but also as housekeeping) and discovered I'd added dozens of screensavers and found crap in the library from demos I'd deleted long ago. At one point after rebooting into OS 9, I discovered another load of leftovers that had .filenames or .foldernames which were invisible in OS X.

If your drive is nearly full it might account for performance slowdown. Figures vary by drive capacity, but IIRC, if you have less than 15% or <800MB free space, virtual memory will sometimes fail to dynamically clear built up cache from apps, eventually slowing down the machine as it pages and swaps itself into a low disk space warning.