I used CS in Rio de Janeiro a few weeks ago - my first time couch surfing (well, with strangers). It was great. Added a lot to my experience socially and culturally. My hosts took me out to a local pub to watch a football game, and to a samba party. There's an ebay-esque feedback/comment system on the site, and profiles can give you a basic sense of whether someone will be a good match for you before you request a couch from them.

I would highly recommend it to anyone to try regardless of age or usual travel preferences: I love flying in premium cabins but hate high end hotels when traveling solo, they're too isolating, but prefer something cleaner than hostels. This is a really good way to meet people and keep costs down.