How might teachers use social bookmarking in the classroom?

I think that it would be beneficial to the teacher to use social bookmarking for their selves to be able to continuously collaborate with other educational professionals. As for students, I do not think that it would be very helpful since all the students would have a facebook etc... account. The only way that I can think of that a teacher could use this strategy in the class would be a lesson on cultural geography and the students could bookmark students from other countries.