Couchsurfing

Coursurfing.org is a very interesting site.  I'll give it a brief review here:

The Good:

• Great UI (except for one thing; see below) - Appealing colors, easy to navigate, all pertinent information is on the front page.
•  A group for everyone, literally.  I found one group that likes French cooking, one that likes English soccer, and one that likes to kayak.
•  Lots to do, even if you don't want to share your couch.  CS is a lot more activity oriented than things like Facebook.
• It allows users to browse through profiles, something most social network sites don't allow.
• Facebook integration saved me from creating yet another login.
• Amazingly international.

The Bad:

• There is no simple way to find people. I literally stumbled upon another teacher at my school. Finding D.I. took about 30 minutes.

Overall this is a good service.  I think this is one I'll be sticking with over the years.