Ignore exchanges where there is 0 trading fees like the big one in Korea.

I do not think it would be difficult for someone to setup a website and scam newbies into buying 'bitcoin', handing over credit card info and taking wire transfers. Perhaps even act legit to start and then segue into only processing part of transactions as real. Quite a ponzi. I don't think is a stretch either. There isn't anything comparable that people would give you money for and the key really is the overwhelming interest and publicity combined with people who have no clue what they are buying. As long as (as with any ponzi) people don't withdraw more than they actually have this could go on for quite some time. Madoff had it much much harder.