Google+ is Google's attempt to lure Facebook users to its own social network site and of course there are learning and teaching possibilities: Professors consider classroom uses for Google+ (thanks Oliver for the link)

I think the biggest potential is in the easy-to-use group video tools - although I haven't had chance to properly try it out yet. If you're already in, let us know what you think of it. If not and you would like to try it, let me know and I'll send you an invite.