Christian Century blogger Adam Copeland has a nice little piece on being a pastor and using facebook, titled "Facebook Rules for Pastors." It has application to just about anyone who has a "public" role. Here is one especially nice paragraph:
"Pastoral ministry is a public calling, and in our social-media age this calling extends to online identities and relationships. I laud the possibilities social media presents and urge the church to use the tools for the kingdom. But just as church-owned houses offer particular challenges to a pastor and family when members drop in unannounced to fill the fridge with makings for the women's tea, Facebook offers the challenge of unclear and ever-changing boundaries."
You may read the whole piece and responses at http://www.christiancentury.org/blogs/archive/2010-10/facebook-rules-pastors