Just interested if someone else is experiencing these problems?
In my opinion it isn´t a hardware defect but a problem with the NVIDIA drivers and Lion.
I also contacted AppleCare but they don´t know the problem and seem to ignore me right now.
Although i´ve found many websites where people are talking about this issue.
The latest entry i´ve found goes back to July 5th, 2011 (so this error also occurred in the GM of Lion) now there has already been an update (10.7.1) and the error hasn´t been addressed. Moreover Apple seems to disclaim it.