A great screenshot from Twitter (via Tweetdeck's iPhone app) that shows the virality of Foursquare. I've spoken a lot about the power of conversation in the real-time web - but this is notable because it taps into the power and influence of social 'gaming', reputation and location-based activity. Within a couple minutes, two prominent Twitter users separately announced the transfer of Foursquare mayorship at a New York coffee shop... one was proud and one was defeated.
By the way: if you do not already, I recommend following Jon Steinberg (@jonsteinberg) and Fred Wilson (@fredwilson) on Twitter.