That is of concern, I'm just testing the water right now out of curiosity. I just don't want to wear out my Radeon 7970 running it everyday and if my card goes out I want to be able to make sure the card pays for itself. My 7970 is sitting at 545 Mhps at fullpower, granted I've down-clocked my card so that it doesn't get to hot while I'm gone. There's ASIC miners coming out i.e. 60Ghps miner for $1299 so it seems at that point the casual miner has not point in messing with Bitcoin mining.
My thoughts exactly. I think that you'd need to get specialized chips for bit-mining to be worth getting into. It's not idle for doing it with graphics cards anymore AFAIK.
Still, so long as you keep temps under control, it should really damage your card.