MySpace and Friendster made a bunch of people money years ago.Now Facebook is a multibillion dollar company. I've been on all of these sites at some point or another, usually so I can stalk lady friends.
The downfall of all of these sites are usually correlated with advertising showing up, flash games, spam, etcs. It's a cycle. One that I currently see Facebook going through. In five years, I doubt most of us will be using Facebook still. We'll have all moved on to yet another site. The internet is a fickle beast, with a three year attention span. (Don't believe me, remember Napster, AIM, Limewire, Yahoo! Chat, Yahoo! Games, Yahoo!, Ask Jeeves, Mapquest, Netscape, AOL... yeah, the list keeps going)
So, the new thing everyone is talking about is Google +. Right now, its basically all the cool things about Facebook, without the Farmville games or advertisements.
Google is the greatest internet company around. My blog is hosted by them, my email is hosted by them, I have a calendar through them, I have tons of Google Documents saved to the internet, my phone is Google... really, if Google wanted to ruin my life, they could with a few clicks of a mouse.
I'm still figuring out Google+, but it seems to be pretty easy to integrate everything Google I have. Only time will tell if it'll stick, or go the way of Google Wave.