"A Source close to Sony" has reportedly revealed that Gran Turismo 5's more recent delays are owing to the implementation of support for 3D tech and the PlayStation Move controller.
It would make perfect sense. Series creator Kazunori Yamauchi has himself spoken of his interest in the two technologies. "We're always attuned to new technologies. If there are display devices or peripherals that seem interesting, I'm sure we'll work to support them," he said in an interview last month.
Exactly when the game will come out is still unknown, but an announcement is expected at E3 after Sony Germany's product manager commented: "The next time we announce a release date we'll be one-hundred per cent sure that we can hold it and won't make the mistake we did with the March date. You just have to wait a little longer until we announce a new date, only some days...or weeks"
So he doesn't really know either...