Needs better collision detection.

Assuming that the stairs are not meant to be a slide/conveyor belt, they should have larger bases (standing on a step is rather tricky).

Obviously, the collision detection needs some improvement. If you're not already using it, I'd recommend finding a copy of Grant Skinner's (gskinner) CheckForCollision script.

Lastly, the character becomes stuck in the walk animation, occasionally (usually when trying to climb the stairs).