Foehn, I think you will probably find the cause of your problems was this package introduced on 13 April:
nvidia-graphics-drivers (295.40-0ubuntu1) precise; urgency=low
This new nvidia driver is known to cause serious problems with performance and stability (compiz crashes); bug 982710, bug 980298.
I'm not sure we've yet triaged all the bugs relating to nvidia 295.40 accurately enough though.
Foehn, I think you will probably find the cause of your problems was this package introduced on 13 April: graphics- drivers (295.40-0ubuntu1) precise; urgency=low
nvidia-
This new nvidia driver is known to cause serious problems with performance and stability (compiz crashes); bug 982710, bug 980298.
I'm not sure we've yet triaged all the bugs relating to nvidia 295.40 accurately enough though.