I just added tags to a view of my posts - kinda fun. Now I can find some things quicker.
Libraries can use tags in the library's catalog and on their website - in things like recommended lists, book clubs' readings. More and more people love participating. They like to add comments, reviews, suggestions. Then there is a need for organization.
del.icio.us gives you lots of ideas for things you might be interested in. When I clicked on the title of a bookmarked page, I went right to the page. When I clicked on a tag, I went to a list of sites and there was a list of related tags too. I love having all these suggestions. If you click on the saved by xxx people link, you get even more - everyone's bookmarks and you click on a person and get more bookmarks. It's lots of fun.

I enjoyed instant messaging. It's not as immediate as a phone call - you need to wait for the person to respond. However, it does allow you to do other things while you wait. It's good for times when you don't have access to a phone. You don't get a busy signal.
The library can use it when you want an answer, but don't want to interrupt someone, when a reference question is being asked.
I like the idea of a Meebo too.