Yeah, they take deposits. People have a dollar account and a bitcoin account on Mt. Gox. They may fund the dollar account with bank transfers, and they may fund the bitcoin account with bitcoin transfers. I don't know how long people tend to keep dollars on deposit there, but the total amounts are substantial. Apparently there is more than 470,000 bitcoins on deposit at Mt. Gox. That's $8 million at current prices. I am guessing that the amount of dollars is somewhere in the range of that - they've been doing $1.5 million in transactions a day, and most people probably take a few days to trade and then transfer the money out.
Of course, we can't be /sure/ of what they've got on deposit - it's not like they employ auditors, or publish reports, or submit to regulations regarding deposits. All that old economy stuff is for losers, y'know.
Of course, we can't be /sure/ of what they've got on deposit - it's not like they employ auditors, or publish reports, or submit to regulations regarding deposits. All that old economy stuff is for losers, y'know.