(Sidenote: I myself always felt more comfortable getting my potential sources down first before going back and looking in depth at those resources, instead of going one by one; it just seemed to help my future paper take shape early on. I would have loved having this back in my student days!)
Yes, social bookmarking sites are of course also an easy way to just create bookmarks from anywhere. However, I think that teachers can utilize these by having their students come up with a topic first, and then use these to help them find sites that would help them in their research. (if we just tell them to go to, say Delicious, and find sites they can tag, they would most likely just end up tagging facebook pages and other things not relevant to anything educational!). As long as we have them come up with a purpose first, these sites can greatly help them in the learning and research process.