Since gnome is the default desktop for Fedora, I think they give it attention before turning to KDE. I've been running KDE with FC3-T2 though, and except for a few messed up icons, it has been near perfect.
Your crashing sounds like it might be happening when your screensaver comes on. If so, you may have it set to use random screensavers, and when it picks a GLX based one, you probably don't have suitable GLX support up and running yet, so it crashes X, which makes it seem as though your system has frozen. Try turning off screensavers, or choose a single one that you know works if this might be the problem.