I'll be the first to admit I haven't been all to nice on the clutch - learning manual on the car hasn't helped (and I'm still learning to rev-match for downshifts). However, the clutch has been alright to me - I caught it slipping once in the middle of a particularly rough bit of driving, but it caught right back up.
Then yesterday, I drove it to school (it was in the 30's out) after letting it warm up for several minutes. The whole way, I was getting problems every time I was accelerating with the clutch slipping. By the end, I was noticing it less, as I was driving extra-carefully (barely accelerating, rev-matching all my downshifts, etc.), but it still was there.
I drive it home, when it's more like 50's-60's, let it warm up about the same amount of time, and it's fine the whole way - even through I was ragging on it pretty hard.
That was the first time I've driven my car at quite that cold out. What would cause that clutch slippage when it's cold out?