Here are some pics from GT Prologue. The crowds at the moment are only sprite based (2D) but apparently look AMAZING. The run onto the track, take photos and cheer, and its all very fluid.
There is 3D pit crew confirmed, and hopefully by the time GT4 ships (another 5-6 months) 3D crowds will also appear.
IMO, I really think that Polyphony are keeping alot undercover and secret. I think GTP is purely a scam to shut people up about what GT4 is going to include. Considering GT3 contained wet races, it would be stupid not to include them in GT4 as well, yet they have not mentioned it or shown any screens at all! There are apparently 50 new courses (and the five included in GTP are all new tracks, which is very interesting as I would have thought they would have wanted to keep all the new tracks for the whole game if they were going to rehash old tracks, which leads me to believe they won\'t be).