I think it is still quite likely that Facebook could implode spectacularly in the same way that Digg did. It would take longer for their company to unwind (due to the huge number of users) but once the momentum is lost other platforms will have a chance to prosper. The (presumed) forthcoming IPO and the events around it will be interesting times for everyone, I think.
I understand your point. But I truly believe that it's possible for an entity of any size to collapse.
In fact, I think that it is so rare for any kind of organisation to get so big as to dominate (say) 90% of its market that there has never really been much chance to pass on knowledge about how to handle problems at that extreme scale. It might even make you more likely to fail if you get too big.
Maybe I should wait a few years and then write "The History of the Decline and Fall of Facebook" in the spirit of Gibbon :-)
