I'm involved in Couchsurfing myself and have been for over a year - in fact I met me wife via the site so it certainly did change my life. I've myself written a bit about the community and site at eyeflare's couchsurfing articles.

It's a fantastic way to travel and meet people and during my time involved I've made many friends and seen things I'd never have had access to otherwise: Like a nice dinner party last weekend while in Paris.