My library is just starting to starting to use web based social networking, particularly in the area of local history. I'm sure this will be further developed as both our library and community IT improve.
I'd especially like to see networking forums for library users to be able to add their own tags to resources in the catalogue and to have greater involvement in collection development and purchasing.
Online collaborative tutorials could be a fun activity. Something like a small course on taking digital photos and adding them to Flickr and our Local History Collection.