ive heard of people running refurbed video cards with no problem. ive heard other stories of people buying them and them having problems, or ceasing to work within a week. obviously they are more prone to screw up than new ones, so its just a gamble. good luck
edit: its too bad they don't have something like carfax about used video cards heh.
I dont think its a problem. I mean, it'd be better to get a new one and play it safe if you have the moeny, but I dot think its that big of a deal. I havnt heard of many problems, though Im sure that you dont get a 100% guarantee or anything.