I just drove a Minicooper. Here's my quick n' dirty review of the experience:

Pros: Sweet torque horsepower to weight ratio and tight braking. It's fun to zip around in, and really easy to park.
Cons: Cheap plastic interior. The controls feel flimsy and I was worried about breaking them. It was like fondling a fancy blender from Target.
Mixed Blessing: People kept looking at me.
Upshot: I'll stick to my bicycle and renting the cheaper cars from Zipcar.

(Photo: sam.soneja)