Down and Out in the Magic Kingdom has proven to be a defining book for my life. It introduced me to the concept of Whuffie, a reputation currency around the time I was volunteering for CouchSurfing and hitchhiking all over the world. I'd love to work out a system that works in a whuffie way, to indicate social capital. So a currency that doesn't decrease when you pass some to someone else.
I guess the main problem here is a sybil attack. How to avoid people creating multiple profiles?
I already mentioned it here: http://forum.ethereum.org/discussion/461/basic-income
For now I just want to put the idea forward. Let me know if you're interested in building this.