There certainly is potential in using del.icio.us as a research tool. As you mark sites for possible research, you can see what other sites are being used for people with common interests. If I were doing my Master's thesis today, instead of in the dark ages before computers, my research sources might be entirely different. I might have been able to contact people who were experts in my topic area (18th century English Lit) and get more perspective. I don't see a lot of academic research at the public library. Maybe in the future, the library will have more of an Internet presence, instead of just a card catalog. In that case, then sites for storytime or homeschoolers or tax information might be bookmarked for our library patrons.
Our library currently has "weblinks"--maybe in the future those links will be on a del.icio.us site instead of on ours. This might allow for more networking between patrons. Tagging is a useful way to track information but there are so many different contexts that a word can be used that it isn't always relevant. A search for "library" tags turned up many articles about the George W. Bush Presidential Library.