Take it with a grain of salt but according to rumour site FUD Zilla, NVIDIA has an ace up its sleeve to counter AMD's upcoming Radeon HD 4850 and 4870.
The site claims a new performance driver will "significantly" improve the performance of the GeForce 9800 GTX and perhaps some other G92 cards as well:
Nvidia is doing this simply as with current drivers Radeon 4850 and 4870 are getting too close to 9800GTX performance and Nvidia wants to make some stand.
The performance might be so good that internally Nvidia calls it 9800GTX+. If we see some big improvements that will clearly mean that Nvidia was holding some performance potential back and that it was waiting for the new ATI card.