IMHO it will be related in a way that it will still be around replicating social interactions offline online.
The way i predict success in online businesses is how well they can replicate real-world actions and dynamic. The bigger and better the set of real human actions a startup can build a online counterpart for, the stronger it becomes.
Facebook is building online equivalent of verbs or actions you can do with people. so the more verbs it can do the more unstoppable it becomes.
What if someone can build the Facebook+ phone? i would also bet on that.
This may be the standard answer for x-killer in any useful product talk.
but facebook is a social time sink. we all seen many came and go. in brazil facebook is just now dethroning Orkut. wich had just before dethroned photolog, or something.
They are all the same. it's just the latest momentum.
Facebook just overcome them now by sending more lobster-trap-email-spam then any other managed to send before.
So the answer: it will be any other social time sink clone (they're all the same as friendster or other anyway) that manages to send your friends SMS every 5seconds.
