The original release date was December 09 but it was delayed because they wanted this game to be as good as it could get. Next release date between March and April.To keep up with the latest news head to Gtplanet.com I'm sure the game will be worth the wait :)
I have heard the reason for the delays is down to getting the on-line racing sorted. Could they not release it in 2 stages, the game then the game with on-line racing ? Many more delays and all the cars will be out of date.
Look out for the E3 conference in June - release date expected to be given then. Most think it will be October/Nov - delays have been due to 3D, damage and some think Playstation move which may inclued a head tracking facility.