I used to teach a course in Second Life in 2007. The learning curve was way too steep for the content. I did not want to TEACH Second life, I wanted to teach the content within Second Life. But my students (even though our first two sessions were F2F) had so much trouble just navigating the world, it made it frustrating for them, and nearly impossible for me to teach them. The platform got in the way of learning.
Just an FYI, many schools have tried to do this. You might check with the Lindens to see if they have kept records. Just off-hand, Harvard and the International Society of Technology Educators taught classes in SL, but no longer do.