Tagging is another one of those Web 2.0 things I've just never gotten into. I tried to use the Firefox extension Del.icio.us for tagging bookmarks, but I felt it was too cumbersome. I now use another Firefox extension that keeps your bookmarks saved to an external server, so you simply need to log in to an account to retrieve your bookmarks just as they appear on your home computer.
I think tagging can be useful for pictures and even for blog posts, but I never actually use it. I prefer using text based searches when I'm looking for something specific. For example, I used to tag blog posts, but I realized that I never went back and clicked on the tags, so I was really wasting my time.
I could see how tagging might be important if I was creating online content for others to use however. Tagging could make information much easier to reach for students looking through a large website. It's certainly something to think about.