You must have 100 posts before your karma even counts. Check out George Spellwin's anouncement at the top of the message board. He tells you all about it.
I think you have to give karma to 20 other people before you can give to the same person. Also I think you only have so much to give out in a 24hr. period. But if somebody did try this they deffinetly have to much time on their hands.