From the iLibrarian comes this article on a company that has Facebook Fridays! They are an encouraged to spend an hour of work time updating their Facebook profile, making contacts, and talking to co-workers.
Although this article is referring to a business, the same could apply to libraries. Public Libraries with multiple branches could keep in touch with each other, see whats going on with their co-workers that they might not see more than once a year. Smaller one person libraries can use Facebook to make contacts with the outside library world.
How many libraries I wonder are already doing something like this?