It has never happened to me after a party either either, thankfully. When it DOES happen to someone, its usually in the scenario I mentioned. It's not a very common occurance, but it's common enough that we have a name for it. I had this one guy that came into my ER who had taken strong sleeping pills and his body couldn't wake him up when his arm went numb. He ended up losing his radial nerve from the elbow down, and couldn't extend his thumb, index, and middle fingers. Unfortunately nerves regenerate at the rate of 1mm a year, and there's alot of millimeters between the elbow and the fingertips.
Here's a good source of info:
http://www.ncemi.org/cse/cse0919.htm
I don't think anyone who has posted here really has much to worry about, but Macattack asked it was possible to do permenant damage. And the answer is yes, it is possible, but it's uncommon.