a world of friends

Ever since I discovered the web I have been fascinated by the whole business of making friends around the world (lets use a wide definition of friend here).
Recently a friend on Facebook suggested that, as a group, it wold be cool to use each others homes as holiday destinations (staying as guests). This reminded me of a similar suggestion some years ago on Bookcrossing. At that time I recall someone saying that it would be safe to stay with another bookcrosser because we were all literary people and therefore safe!
Yes, it's great to have friends around the globe and I might even go so far as to say I would love to visit one or two (in fact I aim to do so) but to trust someone on the basis of their love of books?
I'm sure I'm not alone in having past experiences of 'friends' which were not entirely pleasant and were , on occasion, frightening