The (so far) ever increasing popularity of Facebook, coupled with the fact that journalists have started to write and broadcast about it, has helped to propel it into the limelight. The big stories seem to be its security settings, the myths and controversies of its founding and founder, and general interest in it as a social phenomenon.
It's a place where people meet and talk, so it's a place where there should be a church presence. Encourage your members to sign up if they haven't already, start a Facebook group for your church, and make Facebook friendships one of the ways you keep in touch with people on the fringes, and maybe meet new people too.
Twitter is another high-profile service, interesting and useful for finding out what are the 'hot topics' in the public consciousness.
Added: October 2010