I would definitely agree that a character's powers are important to their character, but I preferred to think of it in terms of the effect it has on them. Take my character, for example; what I find compelling and what I want to explore about Nick aren't the nitty gritty mechanics of his powers, but rather the kind of person they have led to him becoming, the things that have happened to him as a result of them, the way he lives because of them, and so on and so forth. That's the sort of thing the RP's about, I think.

Although, on the subject of actively exploitable power weaknesses, perhaps someone could help me come up with one for my other character, as I've hit something of a block. The power, in essence, allows her to turn off friction and slide around at high speeds - it does this by projecting a field close around her body (so it also works on skintight clothes), which doubles as a minor shock absorber so that she doesn't immediately die when she crashes into something (still hurts, though).

The obvious weakness is that it's difficult to control and not really as good as just flat-out super speed, but I'm not sure if that's enough, so. If anyone has any input, that would be appreciated.