In the Ripple system we have two types of currencies - ripples and all other currencies useful for transacting with people in your web of trust. Ripples are the only currency in the system that can be used for paying transaction fees and transactions between any two users even if they are not connected.
With the discrepancy between the supply of ripples and the size of the fees, spamming the system would be virtually free. This usefulness of ripples is thus moot. Trading between any two peers could be accomplished with Bitcoin, so this use is also limited.
So, with that in mind, what use are ripples really, asides being a way for the developers of the system to monetise?