I originally only new of it through sci-fi art. About a quarter through reading it as we speak.
It's official though, Pixar is currently working on the screenplay for an adaptation of "John Carter of Mars". It'll definitely be a big change of pace.
Apparently they haven't decided if it'll be animated or live action. The animation nerd in me hopes all animated, just because it'll be such a brave challenge to try and pull it off in that medium. What with this and the live action film Brad Bird's doing, the princess archer thing, and Wall-e coming out in a few weeks, I really think Pixar's trying to push the medium out of the kiddie-safe thing. Naive as that might sound.
If they do this project in animation, I really hope they get Bill Pressing to design the princess. His sexy girls are so cute, charming and have such an appealing flow.