[zAy0LfpBZLC8mAC]

Well, what pretty much rules out that MtGox will be considered a ponzi scheme is that if it were, "ponzi scheme" would essentially be a synonym for "fraud".

Suppose MtGox wasn't a bitcoin exchange, but rather sold cars, which had to be ordered and paid for in advance. Now, suppose further that the CEO "stole" cars from the company and then bought new ones using the money from new customers when he needed to deliver a car to one of the earlier customers. That's just plain old fraud, not a ponzi scheme, and it doesn't become a ponzi scheme just because it's money instead of cars - and in particular, you as an earlier customer certainly are not liable for the losses of later customers.

edit: I mean, MtGox under the assumption that the loss was not due to a technical problem, if it way due to a technical problem, it's obviously not a ponzi scheme anyway.