Join ’em! I did. With a new tech-savvy school district superintendent’s blessing, I created a Facebook account for my campus. Due to privacy and security issues, social media sites are blocked at school; however, using FB as a “page” instead of a person is now open.
Some things to consider:

Post current relevant news. (My goal is several posts a week.)
Remember to keep a list of students with parents who DO NOT want students pictures or information online.
Try to avoid trivial posts, but do post upbeat events and pictures.
Model copyright use (no music that is not royalty-free, etc.).
Remember that once you post a certain event (Students of the Month, for example), you have set a precedent! Only post what you plan to maintain.

I am sure we will all make mistakes while learning this new medium. I think it is important that whoever is the “social media” person on a campus (librarian, principal, or other interested educator) be someone who enjoys public relations and has a desire to learn about best practices of social networking.

Today, my email was cluttered with a conversation about a school district that is now banning FB because of some recent problems. Teaching students about user-generated content is new territory. Critical evaluation of who to friend and follow will most likely be a popular and important topic for those interested in education.