Given the potential for independent learning it would seem simple for students to get a little coaching on the interface and be free to explore. This might be the case. I am not sure that this is the way most environments are being used. Do avatars really respond to environments in an authentic way? Could I engage another avatar in a conversation about the color of the leaves on the trees? In a store, how would another player react if I asked how she liked the cut of the dress on the mannequin? I would have to pursue these questions before making any decisions about the real value of the resource. It may be that people are merely interested in socializing in a way that is actually external to the game. Not that that would be a bad thing, but that would be a very specific kind of language use.
Would it be possible to take a class to a soccer stadium, teach them the appropriate vocabulary for communicating during the game, take a tour of the facilities, and then play a game? If so, I can see the potential, but the instructor needs more knowledge of the tool than I can claim at this point. I'm not sure now is the appropriate time to gain that knowledge, but I've had my taste and will probably revisit Second Life in the future.