Well, the 997TT is just a $70k platform gussied up to ... $130?

I happen to agree that they don't really compete. We've probably seen most of the debates in the universe where a person is considering one vs. the other.

The 911 is, to me as to many above, a sports car from the ground up. It happens to have a (relatively) huge engine for its size and weight vs. most cars of its ilk.

The M3 is a 4 seat sedan (or coupe). It combines outstanding performance with great practicallity. It can really be a family car, so long as your kids are young or you never take them far. In fact, when we were a two-car family and the kids were little, my drive was a 325 convertable. I could always pickup the kids from school, with a couple of friends, or drive the family to dinner or visiting in my car. The kids are grown and gone now, and (mother in law not withstanding), I don't plan to utilize the back seat of the 911 very much.