You know it's easy to poke fun at this, but they are a gigantic fucking website. They are in a position to be beat the giants at everything. Google: search - Facebook can create a better search using the data it has about people and beat them. Microsoft - software, Facebook can add it's social aspect to software for phones, pcs, whatever in any way imaginable and beat them.
Facebook is in the position to rule the world. To be what others have imagined but could never have been, to tie it all together and make more money than god.
I'm not saying they will, but underestimating the skill, the determination, and the savvy of Facebook is probably likely. Of course there maybe some bubble mentality in the people bidding, but perhaps these people are in luck and it's not a bubble at all.