I made about $100 off it until it became not worth it. Unless you have a top tier AMD/ATI graphics card, don't bother at this point.
Basically, right now, they only have value because people want to buy them. People think they can exploit a new market for a while. It's just a bubble, and I'm glad I got out before it burst.
I've heard people are using it to buy illegal stuff. I guess there's no authority monitoring the transactions.