KDE 4.3 is out and I’ve been using it for a little bit. It’s better, but it’s still not stable and has performance issues.
KDE 4.0 sucked. KDE 4.1 is what KDE 4.0 should have been, it’s actually usable (for a linux guy). It is still not ready for everyday use, if you want stability or usability. There are still some problems (many of these are not directly the short comings of KDE but of other apps/programs that exhibit a problem under KDE 4), with the most important being stability and speed.