Yeah, rumors are all over the place, anywhere from today to the end of May. The credible release date is mid May (as stated by Senor_Bob). But, the only thing we know for sure is that it isn't today.
Something interesting I noticed was that THG said "Nvidia isn’t sitting still as AMD is preparing to reclaim the performance crown for graphics cards later this month." in their article about the 8800Ultra.8800Ultra Release
We know that they know the true performance of the 2900, but can't speak because of the NDA. Did they accidentally let something slip?!?