Here is one proposal:
http://blog.wired.com/business/2009/03/yes-we-plan-how.html
Their idea seems to be to combine a social networking site with facilities for coordinating action and a karma system. If it can be designed in such a way that signals are honest, karma is fair and the system becomes widely-used, I imagine it could be highly effective. On the other hand, Facebook and co. give free karma that's instantly visible to all your associates, so I fear it will be very difficult for the new site to invade the market.
I'm new here and didn't know if this has been a topic of discussion yet, but I found this story to be fascinating:
http://www.physorg.com/news158928941.html
In short, two psychologists modeled decision-making in a variation of the Prisoner's Dilemma with a "quantum" probability model. Their motivation was to reconcile results from actual studies (the participants consistently made apparently irrational choices) with what classical probability theory predicts a rational agent would choose.
Oh, and the quantum thing isn't new-age mysticism at all. It'...
Yesterday I convered the bystander effect, aka bystander apathy: given a fixed problem situation, a group of bystanders is actually less likely to act than a single bystander. The standard explanation for this result is in terms of pluralistic ignorance (if it's not clear whether the situation is an emergency, each person tries to look calm while darting their eyes at the other bystanders, and sees other people looking calm) and diffusion of responsibility (everyone hopes that someone else will be first to act; being part of a crowd diminishes the individual pressure to the point where no one acts).
Which may be a symptom of our hunter-gatherer coordination mechanisms being defeated by modern conditions. You didn't usually form task-forces with strangers back in the ancestral environment; it was mostly people you knew. And in fact, when all the subjects know each other, the bystander effect diminishes.
So I know this is an amazing and revolutionary observation, and I hope that I don't kill any readers outright from shock by saying this: but people seem to have a hard time reacting constructively to problems encountered over the Internet.
Perhaps because our innate coordination instincts are not tuned for:
Etcetera. I don't have a brilliant solution to this problem. But it's the sort of thing that I would wish for potential dot-com cofounders to ponder explicitly, rather than wondering how to throw sheep on Facebook. (Yes, I'm looking at you, Hacker News.) There are online activism web apps, but they tend to be along the lines of sign this petition! yay, you signed something! rather than How can we counteract the bystander effect, restore motivation, and work with native group-coordination instincts, over the Internet?
Some of the things that come to mind:
But mostly I just hand you an open, unsolved problem: make it possible / easier for groups of strangers to coalesce into an effective task force over the Internet, in defiance of the usual failure modes and the default reasons why this is a non-ancestral problem. Think of that old statistic about Wikipedia representing 1/2,000 of the time spent in the US alone on watching television. There's quite a lot of fuel out there, if there were only such a thing as an effective engine...