some universities have indeed done assigments on second life. Architecture is a great example because people can build things on there. Also economic students have created experimental worlds using alternative economies.
And bear in mind that the technologies students use most often are not necessarily the same technologies they want to use for academic purposes. The email Peter sent around from Deakin Uni earlier this week had an amusingly histrionic quote from a student who said they'd lay a formal complaint if their lecturers ever tried using facebook for posting assignments etc!!
I'm going to the full-day Social Media course next week at University of Auckland. I'll report back on what I find out about how to best use social media in libraries.