Excerpt from a timely Facebook reality check
But Facebook seems to have hit a critical mass. Not only does it have a huge number of users (more than any previous social network), but its audience is spread across every demographic (which wasn't true of MySpace), and they're ferociously committed to the site (nearly half log in every day). It also shows no signs of slowing its growth—and the bigger Facebook gets, the harder it becomes to switch to a new platform. If a storm of criticism surrounding its privacy practices and its frequent, confusing redesigns haven't done anything to stem its growth (and those controversies haven't), I'm not sure what could push Facebook off the main stage in the near term.
The big question for the future of social networking isn't whether Facebook will be the largest and most influential site five years from now. It's whether it will be the only one. Will Facebook be the exclusive catalog of our interests and relationships, or will it coexist with several others?