The CASTLE Project is trying to get 100 school principals to become active bloggers in 100 days. The wiki for the project is at http://principalblogs.jot.com/WikiHome but I think that the single most useful thing at the site is probably the information packet. The information packet has a rather complete discussion of why school administrators should blog in the first place. The discussion document was based on a series of blog posts at Scott McLeod's Dangerously Irrelevant blog.
I'm a firm believer that school administrors should blog. They should do so to create more community around their schools but they should also blog to create a more open atmosphere around education. Too often schools become a sort of closed community - a sort of "black box" - where children are sent to be processed with few beyond their teachers and parents (and not even all parents) knowing what is going on inside the building. We need more openness in the whole process. Blogging could help.
There is a list of the Principal bloggers that the program knows about already of course. Some of them are already up and posting and some are to be created. Also some of them are independent of the 100 Principals in 100 Days effort. If you are looking for ideas about how principals might use blogs this would be a good list to start with.