Cory Doctorow's new book, Down and Out in the Magic Kingdom, introduces us to whuffie:

It's the great conundrum of the web. Why do so many people do so much for free? What do people get out of it? Whuffie - that's what. Coined by writer Cory Doctorow for his novel Down and Out in the Magic Kingdom, Whuffie embodies respect, karma, mad-props; call it what you will, the web runs on it.

The idea of reputation systems that can help to filter information is discussed further on Howard Rheingold's blog, Smart Mobs -

One of the critical uncertainties about the future of smart mobs is whether or not workable, transportable, trustworthy reputation systems will evolve and spread. The potential for collective action in any population cannot be realized until the trust level rises above a threshold, and reputation can multiply the number of ways people trust each other. So far, eBay's and Slashdot's reputation system , or the more geeky trust metric used by Advogato have been the exemplars of reputation management systems.