I was already a member of Facebook before I started web 2.o so this exercise was easy for me. However I am not on Bebo or Myspace (and do not ever plan to be) so I had a look around those sites. After this I have reconfirmed by belief that facebook is the best of these sites. Bebo and Myspace are more for younger people, but it is great if they can be used to encourage people to use the Library.
Facebook is a great tool for keeping in touch and recently it has enabled me to reconnect with friends I hadn't seen for about 7 years. This personal side of Facebook is great and I am very curious to see how libraries will come to use these sites in the future.