As any other social site ever created it seems to be following the same path.
Each month what I'm seeing on my landing page is getting less relevant and more annoying (even without growing my friend base too much and having around 20 friends, I cannot imagine what happens to those over 100). Most of that spam is generated by few active friends, while the rest does pretty much nothing.
Most of communication that I see taking place is very very meaningless, somebody posts a video: "lol", "haha", "nice one", that's pretty much it.
For me it's a socially filtered spam [funny stuff?] site.
If some site can encourage people to have meaningful communication again it will take on Facebook, no doubt.
Get 3 of my important friends on the site and I'm sold. Then Facebook just becomes a big contact list. And at that point I'm not sure where it goes. It might be a contact-list site for a long long time.
Facebook might not die as a website, but competitors will definitely takeaway a lot of value from it. And so far I don't see it becoming much more than a contact-list.
And keep in mind that the less engaged the users are the less ad revenue there will be. I have no doubt that as we're speaking right now users are less and less engaged with the site. Growth is still fast so the revenue is rising, but once that stops it will crumble.
The will have to get more aggressive with ads or people will simply stop to notice them at all. Or perhaps start selling more of the user data. At this point there's not much you can do.
Also the growth they see outside of the western world might be very much junk. I'm in Poland, Facebook craze is already old news here yet I get english ads?
It's great that AT&T has high speed internet for 20$, but I'm sorry, I cannot purchase that here.
Everybody knows ad revenue is tricky. Facebook is no different.
Nobody is going bankrupt, I'm not saying that. Facebook is here and it will stay for few more years for sure, but to compare it to google is crazy. Google can be conquered too I'm sure, but Facebook definitely makes for a far more fragile target.
Personally I'd say it will simply decay and we might not see another social site being that big in a long time to come. Facebook has half of the world on there, cool, but guess what, I am not connecting with those people and never will.
Facebook managed to get a lot of people registered in one place, but has it managed to truly connect a lot of people? Not at all.