In online communities, such as forums, peer approval is conferred in an ad-hoc manner via supportive comments or general consensus being achieved. In the examples below, social networks have adopted a 'reward' feature that one member can confer on another.
Islandoo has Magic Pennies which Islanders can use to reward other Islanders. The help section says that it is only useful if you give it away. I'm not sure whether it the receiver can then pass it on to someone else. That would be cool.
43 Things has Cheers to show your support for an individual goal, entry, comment or photo.
LinkedIn lets you add recommendations (like mini employment references) to people's work profile.
Digg is powered by user-based ranking, so is a sort of reward (src: Dave Wren). I might muse on the value of rewards. Maybe the tangible value has to be purely psychological rather than being an integral part of the system.
In Eric Berne's classic book 'Games People Play' he introduced transactional analysis and the idea of recognition stroking someone ego, e.g. when you meet someone in the street and nod hello to them then that micro-action is a tiny ego stroke, if they then return the greeting then the transaction is complete. When people interact on web communities then they are often in situations of social recognition. I know that I get quite wound up if someone is dismissive of my point in a forum thread + I am partially seeking approval. Seems like a good/interesting idea to build an ego-stroke feature into the system.