From the Comments
ere's my take on Facebook (disclaimer: I work for Google, these opinions are purely my own and not representative of the company, yadda yadda yadda).
Display advertising works best when you have sufficient, quality inventory (publishers whose sites serve ads) such that you attract advertisers in sufficient quantity and quality. Targeting in display ads works because from the publishers, the intermediary has information to figure out what your interests are and so on. A common misconception from fearmongers is that your data is being sold. It is not. Advertisers are paying to have their creative put in front of a particular audience.
The most important strategic move Facebook made in the last few years (IMHO) is the Like button. Whether or not you "Like" things is irrelevant. The main purpose of that "Like" button is (IMHO) as a tracking cookie. Visit any Like-enabled site and you see a small piece of content from Facebook that tells Facebook all the sites you visit. It's a tracking cookie like any other and personally I have no problem with that. Just make no mistake why the Like button exists.
Facebook also has a wealth of information in terms of who your friends are, what your interests are, your relationship status and so on. It's this alleged treasure trove that people point to as the real value of Facebook (combined with the network effect).
I disagree. I think that information is largely useless for a number of reasons:
1. Because of social games and the like who your friends are on Facebook loses a lot of meaning. In the very least Facebook has to filter that information and determine who your real friends are (which it probably does anyway for News Feed filtering and so on);
2. Where people go and what people do is far more accurate than what people will tell you about themselves. As House says--or used to say--"people lie". When you ask someone their interests or opinions it will pass through various filters of what that person thinks you want to hear, what they want the world to believe, what they themselves wish they were and so on. It's a distortion.
It's a bit like dating or job hunting. You look at any online profile or CV and you'll see lies, distortions, omissions and so on. As Chris Rock said, for the first 6 months you're not dating them, you're dating their representative.
Facebook has no search engine. Whatever you say about the size of display ads, search advertising is still far bigger. With search you have intent. People want to find things by their actions. On Facebook ads are an annoyance.
It's the difference between wandering the streets shouting "does anybody want ice cream?" versus putting an ad in front of a bunch of people who have already told you that they're looking for ice cream.
Their mobile presence is at the behest of Apple, Google and (arguably) Microsoft. Mobile (IMHO) poses an existential risk to Facebook, which in part explains the exorbitant price tag paid for Instagram (it has nothing to do with any alleged "bubble"). Much of the engagement on Facebook is because of games. Those games are increasingly going mobile. This is bad for Facebook.
At $100B IPO valuation that put Facebook being worth half of Google with 5-8% of the revenue and significant strategic risks. Of course it was overvalued. It's still valuable but it will take some time to figure out exactly how much it's worth.