I many people that just didn't use email or IM much, but have integrated Facebook into their lives. It's their main way of maintaining communication with many people.
Facebook is a glorified vBulletin and IM client. It's a time waster that most people use to e-stalk or share meaningless information. I think the sooner we drop the mantra that it's "engrained in our lives," the sooner we move on to real innovation. Here's a typical day on Facebook: http://i.imgur.com/ub51D.jpg