Ripple places control of monetary scorekeeping in the hands of the people around us, in our social circles and in your communities. It takes away the excuse, "we didn't have any money in our community," and lets us focus on more fundamental economic and social problems.It might seem paradoxical, but in fact you don't need actual money to be able to extend credit to someone else, all you need is for a third-person to have extended credit to you. So if you have a community where no individual has any money, but they each extend credit to those they trust, then transactions can still happen by trading the IOUs. It's a truly beautiful form of bootstrapping.
It reminded me a little of first-order electronics. A network of ripplers extending credit to each other like a network of capacitors. While they don't allow a flow of money to pass through (c.f. DC voltage), they do allow money to go to-and-fro (c.f. AC voltage) as long as there is no net build-up. The 'impedance' of the network decreases as people extend more credit to each other. When the impedance is high, energy can only flow at high frequencies, or in Ripple when credit lines are small you require small, frequent transactions to have significant economic activity.
Interestingly, Ripple is not dependent on the underlying unit of account. The IOUs can be denominated in arbitrary currencies, and nodes are free to offer 'fx' if they choose. This means you are free to use a sovereign currency like USD or EUR, a crypto-currency like bitcoin or basically whatever you like.
Regarding barriers to adoption, Ripple nicely skirts the main problem BitCoin faces: it doesn't require you to have an obscure asset to be able to start trading, since you can trade in any currency (in fact it doesn't require you to have any currency at all, as mentioned above). Its big problem is of another kind. Transactions can happen only between members of the network that are connected by a trust credit-line (possibly via third parties). When the network is small it is hard for new-joiners to have credit extended to them because they don't happen to know anyone who both trusts them and happens to be part of the Ripple network. Compare with Bitcoin, where as long as you have Bitcoins in your account, it is equally trivial to send them to any address you like. Currently there are around 3,000 'Ripplers', so if there are say 20 people in the world who would extend me USD credit I guess that means there is currently a probability of 1:10,000 that I would get any credit on Ripple if I went looking for my friends.
But it's an interesting concept, so I will write more on this subject soon.