I've used 2psf, as JAE suggests... good idea to confirm with the "carpet supplier," though.
Mike -- interesting... I've typically included a floor finish allowance in my dead load calc sheet... with consideration for whether it's tile, carpet, etc. But I do suppose floors can get refinished in the life of the structure, so I see the argument. I'm not going to worry about my past designs being inadequate or anything, but it's an interesting point. Perhaps I should change my ways. I'd be very curious about what other engineers do as well. Actually, now that I reread it, I'm confused about whether you are suggesting that the code-prescribed minimums include an allowance for floor finish or whether it's an "add," like moveable partitions or something.