As per the FAQ, Xbox 360 users get to enjoy the Dragon Age II demo first, so if you were staying up late (or getting up early) to play it on your Xbox, you can get it now from Live. It clocks in at 1.98 GB.
It should be available for PC in about 7 hours, and on PS3 another 7 hours from then. European PS3 users can't download it until tomorrow.