I think the 26th is a "ready or not" release date. They've got something that works right now. It's not at all what they were shooting for, but they can't delay any longer.
Their yields are still awful (the reason for only having a few 1000 chips) and clocks appear to be about 20% below target. From what's being said, and not being denied by nVidea, the 480 is going to be pushing the 300 watt barrier hard. I doubt we'll see a dual chip version, at least not a reference version, to claim the fastest card prize.
We've seen one small section of the Unigine benchmark released by nVidea and virtually no specs. Not even a Crysis benchmark, at this point, and we're only 3wks from launch.
FWIU, they'll release the cards, be sold out in a few hours, and continue to hold their customers hostage, like they have for the last 6 months, with the promise of supply improving in the 2nd and 3rd quarter. All the time keeping their fingers crossed that TSMC can achieve some reasonable yields. In the meantime the price of video cards is going to stay above MSRP due to lack of competition.
2009 was a great year to buy a video card. 2010 isn't shaping up to be that way. To bad with the new tech available. Here's hoping 2011 is better.