The Facebook story is over. They got ahead in the social network game of making communication over the Internet easier. They did this by making Email obsolete. One centralized system where all users can send instant messages to one another without remembering user logins, email addresses, or phone numbers. This is the ONLY advantage Facebook has over its competitors. And I guarantee their current advantages are going to be eroded away by more open protocols. In the same way that Twitter's current advantage in microblogging is also going to be eroded away.
If you get too far ahead of everyone else you become the target, and there are simply so many startups and smart brains working against Facebook and Twitter at this point that they simply will not be able to maintain their leads indefinitely (which is what their market values are incorrectly predicting).
You're focusing only on features, and ignoring the fact that Facebook has more active users on their site for more time per day and with a higher retention rate than any other site in existence, and that network effects have created an almost insurmountable barrier to entry.
You know who currently has an even better advantage in social networks? Cell phone carriers. If I take a look at my Facebook friendlist or feed, and compare it to the last calls and messages made on my cellphone -- they don't match up at all. That means, at least to me, Facebook's graph for me doesn't relate at all to my real world social network, and so most of its value is probably artificial.
Certainly no system ever built can match Facebook's penetration rate, but it will probably always pale in comparison the real world social network. The difference is mobile devices are going to map a lot better to the actual network in ways that Facebook will be unable to capitalize on.
If you get too far ahead of everyone else you become the target, and there are simply so many startups and smart brains working against Facebook and Twitter at this point that they simply will not be able to maintain their leads indefinitely (which is what their market values are incorrectly predicting).