Gran Turismo 5 still isn't finished. In fact, Polyphony Digital boss Kazunori Yamauchi has made it sound as though it's in the same state it was five months ago, if not longer.
Gran Turismo 5 currently has no release date. Sony announced a March 2010 for Japan at the Tokyo Game Show in September, only to delay it again in January. We've seen heard that it may not be out until autumn.
The game was originally announced at Sony's E3 2006 conference. Polyphony has released some content for PS3 in the meantime in the shapes of Gran Turismo HD Concept and Gran Turismo 5 Prologue, but we still await the main event.