If ripple succeeds I can predict a scalability issue here. At some point transactions will become too expensive and there will be need for deflation in XRP, and OpenCoin will inevitably have to issue more.
It's not difficult to change the scheme from a fee per transaction to a special "fund" transaction that sets a certain number of "prepaid transactions" in your account. You can then perform that number of transactions for no fee. The amount of transaction credits you get per drop could be adjusted by consensus. Similarly, the currency could be made more divisible by consensus.