If I was still on Twitter I'd link to this article by Joel Spolsky with the text, "This." Instead, I'll say that Joel describes the Twitter and Facebook addiction problem better than I've been able to: Birdcage liners
For a look at the mechanics behind intermittent reinforcement that Joel describes there's a book called Hooked: How to Build Habit-Forming Products
. It's as gross as it sounds. However, it does help you look at the products you use in a new, harsher light. I'd use the book as a digital literacy exercise rather than a how-to manual as it's intended.