Anyone with a Quadro mobile GPU, do NOT install anything above 296.88 - the newest 305.93 (that was causing instability on my system) has been just pulled off nVidia site, so they must have acknowledged something is wrong with it.
I have downloaded and installed these new 3xx.xx Nvidia drivers for my GTS 450 too.
At the beginning they would not restart the graphics card after the PC was in sleep-mode (much talked about on the internet too) and the newest of them screwed up my machine so much that the NTFS file structure on my C: drive became so demolished that chkdsk reported "several file errors" and system file check reported "several system files beyond repair".
I am now back to 296.10 and things seem to work normally - except that I have to restore a healthy system image to my C: drive to make it fit again.