LOL, I remember a while back this guy Jimmy and I were messing with a super old junky machine at work...like a Pentium 100mhz. We were trying to get a NIC to work on it, and were tired of rebooting, so we yanked out the old NIC and popped in a new one. Then had it scan for new hardware, haha...
I would certainly not recommend doing it though. We didn't really care what happened to this system, it was REALLY messed up. If I remember, one reason we got tired of rebooting is that it would take more than a few tries just to get it to boot!
If you hotswap a card, you run a high risk of shorting something, and killing your board.