I was in in Washington D.C. this last week attending the National Science Foundation's Advanced Technology Education conference. During the conference, I attended one workshop and one talk on Second Life. Both of the presentations were focused on Teen Second Life, which was interesting, but neither presentation did a very good job of illustrating how I would use Second Life as a teaching tool.
Julian Lombardi's blog has a short YouTube movie that comes pretty close. Be patient, the marketing pitch doesn't last forever.