Does anyone know anything about this movie?

I am a huge, huge, HUGE James Cameron fan and love every single movie of his (including Piranha 2 :chuckle

I have heard only snippets about Avatar but nothing concrete regarding casting or, well... anything Here's A Linky

imdb

Does anyone know anything more definitive regarding the Plot or potential cast? Imdb is more full of half-baked rumours then anything else