This talk Danah Boyd gave distills the reasons why we see a generation divide within Twitter users, and why the most active people on social networking sites (those with the most friends or the most avidly involved in apps) are middle-aged folks, not the youngsters assumed to be early adopters. Basically, teenagers and young adults don't have an ulterior motive or need to network, so these sites are only used for leisure activities and to create an online portait of their social environment.

Millennials and Gen-Yers (born in the eighties and nineties) are on Facebook and MySpace a lot. Boyd says, "For American teenagers, social network sites became a social hangout space, not unlike the malls in which I grew up or the dance halls of yesteryears. This was a place to gather with friends from school and church when in-person encounters were not viable. Unlike many adults, teenagers were never really networking. They were socializing in pre-exi[s]ting groups."

And I think that's what it comes down to: if you're using Twitter for networking with other people you aren't friends with, it's a great tool, because you don't have to be close friends to be able to get their opinion or insight in a flash. By contrast, for the teens and young adults I know (myself included), social networking sites are for confirming initial ties that you will strengthen via instant messenger and real life hangouts. Meaningful exchanges take place in other contexts - via email, phone, or what-have-you. Your facebook page says about you what your seat in the cafeteria does in stereotypical teen movies: what your niche is, who your friends are, who you're connected to, and so on.

Facebook is this generation's iteration of the private phone line with caller ID: with Facebook you can control who you engage with, who listens in on your conversation and how. The privacy aspect of Facebook also appeals to young adults, just like having one's own phone line guaranteed that a younger sibling wouldn't listen in.