The thing about Facebook though, is A) The interface requires lots of care and feeding to stay clean and appealing - Facebook has stayed nice through it small number of very talented engineers. B) Facebook's economics and its supply of topnotch talent has been leverage from its constant growth and its quality as the thing that's happening.
If it instead is faced with a slow decrease in users and a feeling that it's "jumped the shark(tm)", it will have a lot of trouble keeping its economics, its talent and thus the quality of the interface. So I imagine that FB could fall apart in some medium-scale time frame. Oddly enough, I think the end of Facebook wouldn't be good news for those plots "alternatives" to it.
I actually hope Facebook IPOs soon, might postpone some problems...
The iPhone app is worse. You can't even see your own lists at this point, and clicking on youtube links doesn't just play the video, it opens an embedded browser that gleefully suggests that you try adding youtube to your Home screen.
The iPad optimized site is so useless for reading anything a friend links to that I don't even bother clicking anymore, I just wait until I am at a PC.
The message viewer makes it impossible to quickly mark as-read or delete the vast numbers of messages that I never open because the popup notification on my phone contained enough information to never need to open the full message.
The reason that facebook is still going strong is not good user interface or experience, it is that it is incredibly sticky. They managed to become the new email for a lot of people, and that utility is enough to force a lot of people to grind their teeth and ignore the horrible parts.
The problem is that a lot of people have turned number of friends into a high score, but when your friends list is 500 people you barely know, it seems like you are basically using Facebook for the wrong thing.
It might be just me, but isn't this the main use of FB, i.e. stalking? Of course I want to know when my friends have changed their profile pictures, how else would I assess their happiness and fulfillment in life if not by looking at their latest photos?
That being said, I remember the first time I discovered that. For the longest time, I just assumed it would remove only the post.
Odd.
While switching costs are low with search, the ability to offer a better product is difficult. Momentum gives you little advantage in search. For example, Bing is not marginally better positioned with 14% market share vs when it had 9%.
Social networks are almost the polar opposite. It's hard to get any traction at all in social because switching costs are high. But if Facebook sees a competitor get 5% of its user base and then a few months later have 10% they should be scared to death. It probably means Facebook is already dead and just don't know it yet.