I think scams in Ripple will be about 100x worse than Bitcoin. You can essentially invent currency, try and social engineer your way into getting people to believe you have X amount of funds. Gateways (exchanges essentially) will be trusted for a while before they fold and take everything with them creating huge losses because they can invent funds they don't have.
A decentralized financial system based around human trust is pretty ridiculous. Banks work because they have the police and politicians on their side able to protect themselves (which is both a pro and con). People in ripple will nave nothing. I bet thieves would be licking their lips at the concept of Ripple.
Same as GLBSE. Just that this time you call it currency instead of asset. But you don't have to partecipate
Just because someone created some odd currencies (or assets) doesn't force you to have anything to do with them, does it?
The system is more powerful, of course it enables you also to fail in more ways if you take risks you shouldn't. Just be wise and don't take them.
All this issues with trust. Of course the less trust the better, but sometimes you just can't help it. As it was repeated over and over, the most common use case for this feature is to trust an exchange. If you deposit 1000$ in an exchange to buy bitcoins, you trust the exchange 1000$, period. Is it so terrible if you have to explicitly declare it inside the system, since you are doing it anyway in real life?