This post seems to point out that it's a bug in the nVidia drivers, but I got other systems running just fine on the same machine (Debian, Mandriva...). Another relevant page seems to be this one, where they state the bug got fixed two months ago. Am I the only one having this problem on Sabayon?
I'm using the KDE version, my graphic card is a GeForce GT130M. I can post more details about driver versions if you tell me how to do that... I'm not so good with emerge yet and I have to go to bed - I just hope someone got a quick solution since this problem seems to be well known already
