By the way, if you weren't sold on watching Avatar from my previous post, there's one more thing I have to point out.
If you've seen a trailer you know that there's a precious mineral in the ground which is why the Earthers want in. Since it never turns out that its presence is (at least obviously) connected to anything else in the movie, it is simply a MacGuffin.
But what's great is that it is called, by the characters, completely seriously, unobtainium. With a straight face.
This is not something I expect from James Cameron. I would love to find out how they came to decide to use that name.