Kenway's thread on backwards signs gave me an idea for a similar way to handle superheroes.

Randomly generate some weaknesses (defined in game terms), then the player assigns a superpower to each of them (or creates a superpower that combines them all).

Hey Jared,
I saw the headline for this thread and I thought what a cool premise it would be to have a supers game where the characters were slowly losing their powers. Imagine being superman and one day losing you heat vision, then a few days later losing the ability to fly. Could be interesting.

,Matt G.

Jared: I'm not entirely sure how I inspired your superpowers system, but am glad anyway you got something out of my post.

Matt: For more on this, try to find a copy of Orson Scott Card's "How to Write Science Fiction and Fantasy." Most libraries should have one. There's an incredible section about hypothetical costs of magic: in particular, where Mages can cast spells only once or otherwise lose their powers permanently as the story (ie. rpg campaign) progresses.