I just switched neko's desktop environment from KDE to
XFCE. Whoah, my 500MHz laptop actually feels like a usable computer now! Plus, XFCE is rather pretty, in a nice simple way. It reminds me of Gnome, only it does what I want it to, mostly (the only issue I have so far is that the minimum size taskbar is a bit too chunky for my tastes... I'd turn it off, but Nate uses it.)
I have yet to stress-test this by doing some webmastery work on it. However, surely anything has got to be better than trying to work with about twenty windows under KDE, where switching windows takes at least a second, and usually more like 3-5...
[edit, the next day] Turns out it performs about the same as KDE under my work load, and it's missing a couple of features I use all the time, so I switched back to KDE :/