I think we should start a Big List of Information About Mal. Apparently Mal was originally going to be a male coworker of Cobb and Arthur's - go figure.

I don't think there are any fleshed out characters in Inception outside of Cobb, with Saito and Fisher a distant second. Even they are types to a large extent, which the supporting characters (Ariadne through to Yusuf) are for sure. And honestly I don't think Eames is better developed than Arthur, or Yusuf more developed than Miles - they aren't given much attention, and that's exactly how Nolan wanted it. The only place I see him falling down on the characterization job is with Ariadne, but it's Nolan and his female characters' moments in the sun are usually hard won. :/