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