For physical goods, a currency is a value system capable measuring the capital assets, and further for exchange. Similarly, social currency is the value to manifest social capital.
As of today, without widely accepted social currency, we trade our social capital in the same way as in stone age before currency was invented. At facebook news feed, what we see is a transaction log of material-to-material trading such as John became a friend of Cathy, Sam poked Cathy, Cathy joined Green Energy club, etc. The missing part is the measurement and the token of the social value of these social behaviors. How popular is Cathy? How much care can Cathy give to society? If you know Cathy well, definitely you have your personal judgment, in the stone age trading fashion. If you just met Cathy, without a well defined social currency, you have no idea if Cathy could be a good partner working in a community project.
We have a widely deployed reputation system for individual's social capital: awards for achievement, titles, college degrees, resume, work experience, referals, etc. Unfortunately, the system is so unreliable that anybody can easily game it, like Andy Warhol's "15 minutes fame for everyone". Cathy once held a title of Director of Corporate Marketing. However, her short tenure ended with a company PR disaster by her wrong doing. Cathy easily gained "popularity" by aggresive friending to everyone she could find from her facebook account, and in real life, she had zero true friend.
Digital life stream provides a much more complete picture of a personal's social behavior in social context. However, information overloading prevents us from summerizing our judgment into social currency. Personal data mining may solve the problem, if we are able to build a social currency model for data crunching.
Since social value system is extremely subjective to the culture system involved, different communities may value certain social behaviors quite differently. This is the complication of social modeling. Probably similar to financial system, social currency exchange can happen among various culture systems.
Another level of complication is the measurement of the impact of social behavior. Nobel Prize uses time delay to value the most significant achievements. Most awards were granted to the work done 20 years ago. The time dimension was disrupted with Obama's peace prize. Mechanical measurement is indeed difficult. Social currency can be augmented by the impact anytime given the impact is widely recognized.
