[masraum]

If I had to formulate a definition, it would be a car that is quick (0-60 in <4secs), fast (top speed >200mph), with fantastic handling and stopping ability. Besides that, there is usually also a quality of the extra-exotic about them.

Ruf yellowbird, absolutely a supercar.
Carrera GT, and probably the newest 911 GT2 I think would both qualify. THe GT2 has the performance, but the quality of the extra-exotic may not be quite enough.
997TT, I think it's almost there, but not quite. Honestly, it's so close, and they are probably so much more fit to be everyday drivers that they should have their own category that puts them on top, but in a parallel category.