Rheingold on social networks, reputation systems and all this stuff at SXSW:

The question I ask is, What could we do walking around that we can't do now, given a simple reputation system? There's any number of things. If you want to connect with someone who's looking at the same problem, you can do so with a few keystrokes. We all do that. When we're walking down the street, we're surrounded by people we don't know. Some of those people may have common cause with us, but we don't know who they are, and we can't trust them so far.
There's some experiments going on with ride sharing. There's a big payoff there. If you're a big company like Boeing with 70,000 employees going to the same place in Seattle, you're paying the city a lot of money to pay for the wear and tear on the roads.
But the thing with reputational systems is that only geeks change defaults. The ability to coordinate and find common cause with people goes beyond selling a bike or finding a date.

I appreciate the take on ride sharing, it's something I was thinking about.