^Bitcoin doesn't have margin calls because you aren't trading on margin.

Yes, you can get Forex mini accounts, they're all with market makers where the price you trade is determined by the person holding your money. Even with the few really reputable companies, that's just not a good situation to be in.
That's the EXACT same position you're in with Bitcoin trading, which was the point I was making. At least with a FX bucket shop you've got the law and regulatory agencies on your side, not to mention the fact that you're trading with a real business and not some dude with a server in his mom's garage.
While I'm nervous about the fact that trading on Mt Gox means giving them my USD/BTC, I thought trades were direct against other traders, and they charged commission, rather than trades being with Mt Gox themselves?