As a racing fan, I love the Gran Turismo series and can't wait for the full GT5 to be released. As things develop, we've been hearing that there will be improved physics, car damage and visual effects. This has been confirmed by GT head Kzunori Yamaguchi.
Specifically, improved weather effects, car damage and night time driving as well as weather changes were touched upon:
“We are also working flat out on a realistic graphic representation for rain and night,” he noted. More importantly, however, Yamauchi also reiterated that car damage will be present: “And damage to racing cars, we will soon be able to simulate.”
Gran Turismo 5 has yet to have a solid release date, with recent reports pointing to a late 2009/early 2010 launch.
Source: Playstation Universe