[cubeboy]

Maybe its the progression of the web as a communication medium vs fads. Initially there was geocities and webpages, then blogs came along.

The next step was Myspace with its Geocities like system, but actual network style functionality. Along with the rise of the social network ecosystem was user-gen content websites and comments. Comments on blogs and discussion forums mixed with shared links pushed through 4chan, forums, and then Digg.

Along with these useful mediums was also the fad like rush. If its cool then you have to use it. Myspace was to ugly though and Facebook brought along format, and styling, like the Apple way.

Facebook has some brilliant underlying concepts - Events and Messaging mediums in an online world. Much better than email and sms.

There are also several layers of society and how they interact. The social to be social groups, and the not so noisy users who like it when they visit a city can see old mates.

Facebook will still be the top web-based social communication medium (besides email for business). When HTML5 comes out and web-gaming increases more, you'll see a bigger explosion of Facebook usage I think.