hmm.. i was going to comment on forza vs. GT, but it seems the discussion has turned to NFS vs. GRID.
I like GRID. It's arcadey, but it's fun. I use a G25, but I set it to just 200 degrees and don't bother using the clutch or H-pattern.
I'm hoping SHIFT has good sim physics. I'm a NFS fan (since NFSII back in '97), and I'll buy it with whatever physics but NFS usually has a good list of cars I wish I could drive with simulation physics that we don't get in GT. Most notable Porsche and Lamborghini, plus a few that may or may not be in GT5 (Exige, Camaro (2010), McLaren F1). I know Forza has those, but I don't have an Xbox, and I'm not buying one to play a race sim that doesn't support a good FF wheel like the G25. I just don't see the point of meticulously modeling the physics of hundreds of cars for a simulation game when they can only be driven with your thumbs. You people who use a wheel know what I mean. If the Xbox/Forza supported the G25, I'd seriously consider getting it.
Oh my, there I go rambling on again...
If SHIFT gets the physics right, the next NFS (after the Criterion one) should use the same physics, but go back to open roads/free-roam city + police chases. We have GT (and LFS

) for racing. We need a police chase sim.
EDIT: As far as the thread topic is concerned, I don't see how GT and Forza are competitors. That's media hype. I have a PS3, so I buy GT and don't care about Forza, however good it may be. If I only had an Xbox360 I would wish I had a PS3...I mean I would get Forza. If you have a PS3 and an Xbox, you can probably afford both games. The real competition is console sales, which is genre independent. GT5 could be up against any Xbox-only title with a similar release date.