Nvidia GeForce Graphics Card Blue Screen of Death crash
Solution 1:
After some googling I found this thread of people having the same problem. There, disabling hardware acceleration in Flash seems to help.
The other suggestion was to downgrade the driver, as it seems to be a conflict between newer Nvidia drivers and Flash Player.
You could at least ease some symptoms by enabling HTML5 video on the sites that support it (e.g. YouTube, Dailymotion). Or you could use something like FlashBlock to at least remind you before you load any Flash content.
Solution 2:
My GTX 470 has been similarly unstable for a while. I was suspecting bad memory, but I came across this post on Nvidia forums suggesting a mild overvolt to make the card more stable. I know the bug description says it's most likely not a hardware problem, but I'm putting my 2 cents here since it might at least help others.
In short, I used MSI Afterburner to increase the Core Voltage ~0.13mV above default, and my card has been much more stable since.
Your mileage may vary. Remember that more voltage likely means more heat and careless fiddling around may very well damage the card further. I used it as a last resort since my problem was bad enough that I would have had to ditch the card otherwise.