The half-life of "cool" is very short. Facebook started out as a hangout for college kids, and then it became the cool alternative to MySpace. But now, when parents and grandparents are using Facebook, is it really cool anymore? If boring corporations like enterprise software companies have a presence on Facebook, that would also seem to detract from its coolness. At some point, when everyone is on Facebook, not being on Facebook will become the cool new thing.

I think that buying Instagram was a clear signal that if something cool-er comes around the corner, we will buy it. that is, unless they try to buy from another Zuckerberg.