I admit I'm very impressed with Robert Downey Jr's sounds as Chaplin. He's great.

He may have a natural ability for that sort of thing, but he certainly had to learn and work on these things for the film. I recall a quote (from his page on here) where he says: "When I accepted the part, they didn't tell me that I also had to do the acrobatic stuff of Charlie. That has cost me a lot of blood, sweat and tears."

Never finish what you can't start!