Sony confirmed that Gran Turismo 5 has been delayed until either the "holiday season" or early 2011. Here is the official announcement from their blog:

"We sincerely apologize to GT fans for the delay, however, creator Kazunori Yamauchi and the team at Polyphony Digital want to make certain they are creating the perfect racing experience, and we are confident that this ambitious game will exceed expectations when it launches.We'll have more information for you in the near future, but said that it will be coming this "holiday season."

Here is a link to the post on their blog.

Kotaku (Kotaku.com) has found out that while SCEA won't confirm a 2010 release, the Europe arm of Sony Computer Entertainment says the game will be out by Christmas.