Second Life

The discussion about Second Life gives us a look at what might be new avenue for education. I first heard about Second life being used for classes while I was at a conference. The two brief discussions that I heard have left me with more questions than answers. How safe is it? Is there a way to limit access to certain areas? For example, if a virtual class is set up would anyone with a login be able to access it? Has anyone started an education based version of second life that allows educators to have more control?