They still show a trust system like this:

The system works because everyone along the path has vouched for the person just directly before him in the pathway. He accepts an IOU from her and then issues an IOU of his own for the same amount to the next person in the path who accepts his. His balance then zeroes out and the IOU has moved along one more link in the pathway.

The more people you trust and the more people trust you, the more pathways there will be for IOUs to travel. The more IOU pathways available, the more transactions become possible without a Ripple gateway.




Edit:
This looks great...

Built-in currency exchange
Currency exchange is built-in, allowing people to pay and receive in their preferred currency — including Bitcoin. So you can make payments in BTC even for things priced in fiat, or conversely, accrue BTC from payments made from payers using euros, yen, or dollars. In general, Ripple expands the Bitcoin marketplace.



...and this looks somewhat bad.   

A Gateway will typically:

    Accept fiat from a customer and credit their ripple account balance.
    Accept funds from a ripple account and send the customer fiat.
        Gateways should comply with the BSA, have AML policies and require KYC information.