I found this post from Tim Challies to be thought-provoking. It’s worth a read. Here’s an excerpt:
As you consider using Facebook in your ministry, or as you consider how you are already using it, spend a few minutes thinking about what Facebook has replaced. It is generally true of new technologies that they do not just add something to life, but that they also replace something that is already there. In the case of Facebook, it may well be that it is replacing real-world face to face ministry. Facebook builds social connections and in some ways enhances them; but it can just as easily diminish them as it replaces offline life with online. There is always the temptation to take the easy route (Post “Happy Birthday” on someone’s wall instead of calling him; Send an email instead of meeting him for lunch). Be sure that you are not allowing Facebook to be an easy way of getting around difficult ministry. And make sure you are not using it to disincarnate yourself, to remove your physical presence from people’s lives.