"I think the younger generation doesn't have an expectation of non-invasiveness yet. They just aren't doing anything important enough to be bothered when interrupted. I think that changes when you get a little older."

I'm 27 and this rings true for me. I use to have IM enabled all the time, and work on some things in the background.

That's no good for things I'm doing now, and I rarely chat idly on IM.