IMHO, the biggest opportunity for scamming is the large scale DDoS attacks on the exchanges we've been seeing lately. I believe these to be orchestrated events by organized groups with access to large resources and are using BTC as a pure speculative market. Think of organized crime and investment banks. They engage in the DDoS attacks in an effort to manipulate the market and get their orders executed. I would imagine the savvy algorithmic traders and hedge funds are engaged in these practices as well.

The way to stop it is for the BTC network to get even more distributed and even more liquid (needs to be used for more transactions and not simply as a store of fiat currency value, but a value store in and of itself)