Unlike some I'm not convinced that facebook will fail. However, I think the risk that they will lose a lot of their userbase and/or they will fail to massively increase per user monetization over the next, say, 10 years is pretty high (maybe 50/50 as a SWAG).<p>The advertising revenue risk is a big one, but there are bigger ones I think.<p>First, we may be nearing the end of an era where monolithic social sites make sense. Social Graph as a Service and federated social networking just plain makes sense. I think the biggest risk to facebook isn't necessarily the one big competitor (like google) but a thousand tiny competitors who offer the same full suite of services as facebook but are more targeted toward a particular social niche.<p>Second, as technology advances the ease with which someone can bootstrap a company that has 10 million, 100 million, or even a billion regular users drops dramatically. Right now supporting a billion users takes over a thousand employees and data centers around the world. How will that change in 5, 10, 15, and 20 years? In 2022 it might be possible for a site with the same usage load as facebook to be supported by a company with less than a hundred employees and other expenditures on the same scale as payroll. When, not if, that happens it'll open up facebook to a much greater degree of competition. It also fundamentally changes the game, because then you will have situations where "fad" sites rise up and then evaporate away in a matter of only a few years, months, or days and yet still have gigauser popularity at their peaks.<p>Third, related to the other 2 points, social is just plain going to change, a lot, over the next several years. Anyone who thinks that the way social on the web works today should be set in stone and never changed is either clueless or evil. There is a lot that's missing and a lot that's broken today. Facebook has so much work to do just to be able to increase its monetization to a level that justifies their stock price, but they will also have a tremendous amount of work to do to fix and change social networking. If they do one and not the other they are doomed, but their competitors can get away with doing only one and they'll eat facebook's lunch.<p>Either way, it'll be exciting to watch what happens.