Owen Strachan has some thoughtful posts here and here concerning the use of Twitter (Twitter is akin to updating one's status on Facebook).
Thabiti posts on technology and community.
Josh Harris only lasted a week on Facebook. He updated this post to say that he is now back on, for the purpose of prayer for his ministry, and to endorse his book and his conference book tour. Sort of ironically, the reason he originally left was due to Facebook's tendency to foster self-promotion.
Justin Buzzard offers biblical guidance for Facebook users.