Hold up. I got banned so I'll be objective.
The entire Trailer of GT5 trailer had no physical gameplay. Also the first half was entirely CGI. The second half where the graphic level obviously downgrades is replay mode. To be honest The videos above show Forza 3 better graphically. The cars just look better.
Also Nascar might mean alot in America, but in Europe where GT and Forza 3 will sell better Nascar doesnt mean anything.
And to be honest the whole feature set of Forza 3 is leagues ahead of GT5. Community, customization and HD Video editing. Personally I think Sony pulled showing gameplay of GT5 after seeing Forza 3 yesterday. Because graphically the in engine 'enhanced' replay segment of GT5 looked worse than Forza 3's. The cars are close, but the environments are far more detailed in Forza 3.
This following shot is taken from replay mode just like the GT5 trailer. This is Forza 3. Find a GT5 photo in replay mode actually racing that looks as good. Now this is completely fair to compare these shots to GT5 trailer. As both are enhanced in exactly the same way. Meaning neither look as good in Gameplay. From what Ive seen Forza 3 wins graphics and features. GT5 wins Tracks and Cars out the box. You do realise that DLC can add more cars and tracks right guys? IMO it's silly for Sony to wait another 12 months to release a game with more content than Forza 3 out of the box, but by the time it's out Forza 3 will have had loads of DLC cars and tracks by then.