As already mentioned I am a big fan of Couchsurfing. It came across me for the first time in 2005 when a totally drunk Brit who was being hosted by a friend of mine in Stuttgart talked about it in a bar. Though I only registered in 2007 when my youngest brother and me hosted the first surfers in our shared flat (caused by a relaunch of the CS platform my profile shows 2009 as sign-up date)
The basic principle of CS is quite simple: You host people free of charge at your place and if there is no posibility to do so you can also meet for different activities. “Isn’t it dangerous?” is the first thing what I usually get as a reply. As every member disposed of a profile with references (similar to Ebay) and as there is also the possibility to get your ID and location verified I have the chance to inform myself upfront before taking a decision. Of course nobody is forced to host anyone, there are also many members who are just surfing or using Couchsurfing to get to know people.
The best stories I experienced with Couchsurfers were during my South America trip in spring 2010 when I was guest in more than 10 countries and was hosted in anything between a condo with rooftop pool to a shack. Especially in the poorer countries you will experience an amazing hospitality and the little people there have is shared even with more dedication among strangers.