Obviously a leap motion won't replace your every interaction with your computer, but it'll replace several, especially within visual design and video games. You can't tell Siri how to shape a model in Blender, but you could mold it in your hands like clay.
Waving your hands in the air for 8 hours per day (or even longer if we consider working hours at some software companies) when there are other options like the SpaceNavigator by Connexion available?