I don’t yet have access to Facebook, but this TechCrunch review notes the key element in successful web applications:
Facebook clearly gets the idea of an attention metastream, where page views aren’t the currency that matters but rather how effectively the service allows users to communicate. Facebook users will now have a much easier way of staying up to date on what their friends are up to. It may mean less page views for Facebook in the short run as users rarely have to leave their home/admin page to see what’s going on with friends, but if it makes users love Facebook more (is that possible?), it’ll pay off in the end.
Whether for business or pleasure, information, passion, and interaction are key.