Bug relief

Just in case you have also been bitten by KDE bug 261323 (chances are good if you are running KDE on a multi-core system with an nVidia graphics card and compositing enabled) and are using Kubuntu (Maverick): You can get updated KDE 4.6.2 packages, which include a fix for this issue by KDE developer Martin Gräßlin, from my PPA:

https://launchpad.net/~thilo.ginkel/+archive/kde-4.6.x