I have a IngDirect (now CapitalOne360) checking account, which for many years was attached to Paypal and Google Checkout for receiving payments for Bingo Card Creator. One day, I got a call from their fraud/security department. Paraphrasing: "We know you're clean and well-established with us, but this use of the account with two incoming transfers a day is outside of our risk parameters, so you've got 30 days to move off it for your business use. We don't want this business."
It's highly likely that Bitfloor was receiving many times that volume from many more payers with less history and, let me be charitable here, less ability to convince the fraud department that there was a legitimate business causing the deposits. It was obvious they were going to be shut down.
P.S. If any of you think this won't happen to Mt. Gox I encourage you to consider "How high do I rate my understanding of risk controls and regulation at Japanese commercial banks?"