Update May 2009: A recent study in the U.K. found that, thanks to the recession, 5 million English homeowners have considered becoming 'reluctant landlords' by renting out rooms.
When my friend Michael, an inveterate couch surfer, turned up on my doorstep a few years ago, my boyfriend had just moved out, and I was wanting company and needing extra rent money. Thus Michael took up residence on the couch my ex had recently vacated, and I went about adapting to having a roommate who I didn't want to see me naked.
Aside from having to close doors and don a bathrobe more often than I was used to, my new living arrangement worked pretty well--for a while. Michael was paying rent and lending me a supportive shoulder. We had agreed when he moved in to check in with each other after a few months to make sure there were no major problems, and when we did so, there weren't. So Michael stayed on ... and on ... and on, and I commenced to kicking myself on a daily basis for not having set another check-in (or would that be check-out?) date. When he finally did move out after about a year, our friendship had been sorely tested.