Second Life or Croquet? What do you think?

I heard some intriguing presentations this week about education in Second Life, but I happen know that there is an open-source, free (?) alternative called "Croquet." Do any of you have experience with Croquet vs. Second Life? I'd love to hear about it in the comments. I attended two talks, hoping that someone would compare different platforms, or at least give the audience a chance to ask questions, but no such luck. I think these multi-user virtual environments are really interesting, but I have some reservations about educational institutions making substantial investments in building infrastructure inside of an environment that belongs to a single company, Linden Labs. It would be nice to know why an educational group picked one environment vs. another. BTW - World of Warcraft looks fun, especially when the participants are interviewed about their favorite candidates, but somehow I think it's a little bit too far out there for the audience I'm considering. I did find two articles here and here.