I can't really say for sure whether its taped out or not, but reason could support either answer. For one just because the design is taped out doesn't mean its 100% bug free, just means the design is pretty much finalized and the debugging is in its final stages (especially driver debugging). But also look at the r600's launch, the original r600 rumors talked about a monster card (but all we got was monster power consumption lolz) but ati kept quiet and it turned out to demolish everything previously released by ati, but still no performance crown stealer. So far gt200 is following the same steps, extremely complex and large die, 512 bit memory, rumors of monster. Thing is, usually nvidia gives out a lot more information than this on projects they are confident on. So either they are worried about the rv770 stealing the performance section where the largest sales have been taking place recently (most profit:costs comes from high end though) or something's wrong with gt200 if its not taped out yet. But don't forget, g80 was in volume production months before it launched, so that could mean there are driver issues or samples are still being given to coders, or simply yields are crap so nvidia is stockpiling them. You never know until we actually see a real preview.

As I said, if you think about it rationally based off past events, you could support either arguement.