"CouchSurfing seeks to internationally network people and places,
create educational exchanges, raise collective consciousness, spread
tolerance, and facilitate cultural understanding."
It seems quite simple in operation. Sign up, plan your journey and post it on the website and see if anyone's got couch going spare in that area on those dates. Your not expected to pay the hosts, but you are expected to act like you would if staying with friends, e.g. help with washing up, take out the rubbish and generally offer some help.
Photo by Craig Boney
Members can be "vouched for" by other members, so building up trust. Otherwise the safety risks are really yours to consider. The people on couchsurfers.com will have registered, but whether they've registered real details is another matter. On the other side, those offering their couch don't have to accept everyone on the network.
I like the idea of this, not because it's so cheap - but pretty sure you get a lot more local knowledge and a feel for a place by staying with on someone from the area, plus you get to make friends around the world.
http://www.couchsurfing.com