Facebook is Taking Over the WORLD  

It's interesting that with all the noise about privacy issues that Facebook continues to grow. It definitely isn't perfect from my standpoint. In my opinion, it is the best option for social networking at this point. Myspace is too cluttered and ungainly at this point. Twitter isn't as a fully-featured social networking site but serves its niche role.
It would probably take a huge game changer, either competition or a major mistake by Facebook to bring it down.
I think that AOL manages to stay high on its position because there are quite a few people who started with it in the dial-up days. I know some people who use AOL out of habit rather than believing it is their best way of interacting with the internet.

Although Facebook is huge in popularity, I think that within the next two years, it will begin to slow down. I feel like a lot of the first users of facebook are starting to get bored with it and are moving to other, more exclusive social networks such as Plurk. Also, with the huge movement in marketing and doing business related activities on Facebook, more and more people will start to move away from it. Maybe not delete accounts, but at least become less frequent visitors to the website.

Both excellent points being made. This is a macro issue in perspective. Once things get too big, people always start looking at the next big thing, almost like a wave. Save for exceptions such as Amazon and Ebay most other sites have had their ups and downs and I think that social networking sites may actually split up into more specific and more exclusive networks. In other words, we want privacy, we want exclusivity but we also want it in a massive corporation. This is never going to come together the way we want. The majority will stay with Facebook but a significant number will migrate out to more specific walled gardens.