I have to say a a racing game fan I am really looking forward to Forza 3. The live demo 1 TRack 5 cars has been very entertaining and competive already.
Its not worth arguing over the GT5 vs Forza. They will both be great, but Forza 3 will be this month, and also be loaded with those brilliant user generated content features that made the previous incarnation so much fun too.
See you on the track!