I don't agree with one of the commenters complaining about eBay - yes its an ugly 1.0 site but:
- I think the star rating was central to their success. It "took reputation to the consumers" in a form that was (mostly) understandable and dissolved distrust of remote buyers/sellers. People forget how revolutionary that was.
- Also the concept of "WINning" an auction was a critical piece of reality distortion that surfaced an emotion that people often don't realise themselves. That reinforcing a visceral experience.
It also reminds me how ever since mint.com - everyone seems to be building green sites - meh.
The emergence of game culture in other ecosystems (foursquare etc) is also another huge wave that will be interesting to follow - will we become fatigued at the endless goals applications/sites start to set for us? Can I monetize my effort, is there a liquid market for "badges"?