DM News recently published an article about trend we've all been hearing about: Teens prefer instant messaging over email. The implication of this is that teens will grow up to become adults, and bring their IM habits with them. And therefore, along the way, email in its current form, will be replaced by IM.
While I'm still a handful of years away from living with any teenagers, I think this trend has more to do with being a teenager than IM emerging as the new "killer app."
Let's step back and look at this. Obviously, some adults live on IM, and some teens swear by email, so what we're discussing here are generalizations. Furthering those generalizations, I propose that being a teenager is a very different thing than being an adult. (Call the press!) Teenagers live in a highly social world and receive a lot of positive social feedback for being active in that world. In other words (and I know I'll get some push-back on this), teenagers achieve social status in their lives primarily through social interactions. Instant messaging supports this, and allows them to reach out and interact with a widely dispersed group of friends with maximum ease.
Now, let's switch to adults. Clearly, being socially interactive provides positive benefits for these folks as well, but incorporates the added dimension of mortgages, families and jobs. While social status is still important, it is achieved as much by apparent income and the trappings of success as it is by "hanging out and chatting." In fact, I'd argue that the older you get (and I do have some experience at this), the more "hanging out" becomes less of an option. Your time becomes extremely limited and, if you want to do something well, you usually need to sit down and focus on it. As Alexander Graham Bell said, "Concentrate all your thoughts upon the work at hand. The sun's rays do not burn until brought to a focus." Managing your life by focusing on one area at a time, especially when put in light of careers, is the hallmark of adulthood, and a tool like email strongly supports this mode of operation.
So, there you have it. Instant messaging is great for an interruption-driven, highly social lifestyle. Email is great for a time-compressed, get-down-and-focus-on-each-project-one-at-a-time lifestyle. I believe that the IM-using teens of the world today will shift effortlessly into being the email-using adults of the tomorrow.