NWN2 is available via Direct2Drive.  You can buy and download it now, and then activate it on release day, but from what people are posting in the official forums, this is not a good idea.  Evidently, in other games Direct2Drive puts out its own patch downloads.  If this is the case in NWN2 (remains to be seen), there could be a delay after an official patch, and you wouldn't be able to play with the rest of us who patched via the official channels.  Discuss in the forums.