I will freely admit to being a Facebook junkie. I find it very useful, especially as most of my friends and family live in other cities, States and countries. It put me back in touch with people I hadn't been able to reach in years (hi, old boys!) and lets me chat with people with whom I would never otherwise have had the occasion to meet.
I have become quite fond of some of the applications, too - but I can save my thoughts on Goodreads, etc., for next week.