I've actually met a few people (and some customers, actually) through Twitter, and one person so far through Hacker News (davidw) - I think a more organised/rigid approach would just be weird. But then I probably wouldn't use an online dating site either if I were single...

Took a swing at this one a few years ago - http://whosgoing.com

tumblr.com - it's slow going finding cool people, but they are out there. use the explore page.

other blogging sites with location services might be helpful as well.

posterous.com

linkedin.com (groups - I'm just as surprised as you)

meetup.com?

but that's kinda rigid (gotta choose your interest category) ... doesn't do the work of pairing you up with others based on a broad range of interests.