Just found this: http://www.1up.com/do/newsStory?cId=3168245
For those of you who don't want to click the link I'll do what Abe does and sum it up:
[B]According to X3F's sources, Forza Motorsport 3 will be ridiculously huge, featuring at least 400 cars and 100 tracks -- so much content that it will take up two game discs[/B
I for one can't wait for it. (If this is true).