I have EXACTLY the same problem mentioned in this thread:
I see that it's a common fact across many 6800GT's, even from different brands (mine is a PNY). The computer sleeps, and when it's back from sleep mode there are some 2D artifacts that are resolved with a reboot.
The poster of the aforementioned thread says it's resolved with "NV5 Rev 2", what's that? A new revision of the GPU?
Good to be back after 2 years away.