I joined Delicious and found it a great way to centralize all of my favorite webpages so they can be accessed from any computer at any time. You may also share your tags/bookmarks with other delicious users.
I can see that this tool would be helpful in research as you can save all of your links to your favorite sites using bookmarks which are linked together through tags. You can also search other users tags to find more information about topics you are interested in. Teachers and Librarians could both take advantage of social bookmarking sites when they want to research a particular topic or when they wish to gather many websites together for their students to use in their own research. They could also create a Tag "cloud" which students could access in order to find info on topics of their interest.