It's not unlike what a "Full Tilt dollar" was back when Full Tilt Poker and PokerStars (and others) where raided by the FBI/DoJ and had their .com seized and si

It's not unlike what a "Full Tilt dollar" was back when Full Tilt Poker and PokerStars (and others) where raided by the FBI/DoJ and had their .com seized and sited unavailable for some time. Full Tilt didn't come back up for weeks... Them months. People on big poker forums would sell / buy "Full Tilt dollars" at a lower price than the real dollar price. People try to determine what's the probability that accounts will be able to unlock their funds: if you're thinking there's a p = 0.3 that Full Tilt will pay back their users (or that there's a 100% probability that they would pay back at $0.30 per Full Tilt dollar), then it makes lots of sense to buy other people's Full Tilt dollar / accounts at, say, $0.20 per "Full Tilt Dollar". A MtGox BTC is just that: it's a BTC that may or may not be real, that may or not be paid back or that may be paid back, but not in full. You even now have people buying MtGox BTC from other users at a lower price than the "real" BTC price (of course there's a issue of trust involved between users buying/selling MtGox BTC but that is another topic). Regarding Full Tilt: all the players ended up getting paid in full. So people who bought Full Tilt dollar for way less than $1 per dollar made a very good deal. For the little story (if I'm not mistaken) Full Tilt has now been bought by PokerStars and is operating again (but not in the U.S.). MtGox has both "MtGox BTC" and "MtGox $". We'll see in a while if they turn out to be equivalent to 100% BTC / $ or 0% BTC / 0$ or something anywhere in between.