Personally I think Facebook has passed a tipping points in its growth/ubiquity which means it will be a dominant player for a time to come. No crystal ball here though, that is just my gut feeling. We probably have over half a billion people now with years of photos, memories, life moments on their account, and that stuff is not easy to just get up and walk away from. Less than 10% of photos of me on my Facebook are actually mine.
You guys are also mixing up the value of Facebook with the value of the IPO. The IPO is very speculative, it is trying to price something completely new and never before seen to the world, a website with a billion users, half of which use it daily, with a time on site of 400 minutes and over a trillion page views a month. We are in completely unchartered territory here and noone, most particularly these finance imbeciles who do most of the talking about it all, have any fucking clue what the future holds, and therefor what it is worth. I remember back when YouTube was a huge money suck and everyone was whinging about the same thing "It's got no monetization future, it's a dead horse, a money sink, you can't make money off people watching videos for free online". Now fucking look at it, big G is making a killing off it and it doesn't look to stop anytime soon.