I recently upgraded to a used GTX 260 (EVGA, type SC; model 896-P3-1257-AR to be specific), for the purposes of playing Minecraft, etc. more smoothly. This has been pretty successful - the GTX 260 gets about 2x the frame rate of my old ATI X800 XL, and is only slightly more noisy (because the fan is larger and runs faster).
But the upgrade was not without problems (since solved, see below). The moment I put the card in I started having problems with hibernating WinXP which had never occurred with the old video card. About 1/4th of the time hibernation would appear to finish, and the screen would go blank, but the machine would not actually switch off. Worse, upon rebooting, the computer would act like it had hung, and discard the hibernation file, instead proceeding to a regular, full boot. It was like my computer was crashing about once a day.
Suspecting a driver incompatibility, I tried several different ones:
301.42 - hibernate problems
296.10 - hibernate problems
285.58 - machine somewhat unstable
280.26 - machine very unstable
275.33 - hibernate OK, but machine is now unstable (most often hanging hard while watching video).
Other recommendations from around the net:
I contacted EVGA support, and they gave me a bunch of fairly basic tech support suggestions that I had little hope would fix the problem, and indeed they didn't. Then they suggested I RMA the card, which I did. Problem solved! The card is now completely stable with out any hibernate problems under the 301.42 driver (I didn't test any others). It only cost me about $5 to RMA the card, because of shipping it back to them. Turn around was super fast - they sent the replacement card out the same day it got to them, and it was in my hands the next day (note, however, both EVGA and I are in S. California).
So to conclude: hardware problem.
Update, again: after about 1 month I had another crash on entering hibernate. That's a lot less than before I sent the card back, but still suggests that the problem isn't actually fixed, as my machine never had this problem with the old ATI card. Not sure what to conclude now.