You have got to be kidding me.. NFS forums is SO active... however the posting quality there is as terrible at the GT5 section here.
There's a small forum I frequent. It's all about racing games...Burnout, Forza, GT, NFS, etc... There are currently 2 people playing it, but if you have insightful things to say, you'll definitely have one person keeping it active with you. I on the other hand only have Hot Pursuit 3 and GT5... the place is less strict on profanity so I'm not going to post it here, PM me if you'd like to see the place.