Correct, there is no coordinated way to do that right now. Because the blockchain is public, we can tell if coins came from a known bad address or not, but ther

Correct, there is no coordinated way to do that right now. Because the blockchain is public, we can tell if coins came from a known bad address or not, but there's no central repository that lists bad actors afaik and the reference client at least doesn't support refusing to trade coins that are "tainted" by a certain address. I imagine the Bitcoin community would be pretty resistant to attempts to establish something like that, since a lot of the bitcoin ethos is based in distrust for centralized authorities.