One site said something about April 13th... I think it's just a rumour started by Nsuckia to buy some time. They know that very few people will spend $500 to upgrade their card for 15% boost in performance. I'm guessing it would perform 15% better than Ati's current cards but knowing Nvidia you will have to use special drivers for this work with benchmarks and games.
And you will have to change drivers for certain games...
The good news is that if they do bring it out, I can get that 256 Pro card for $217 again (stupid Amazon).