One of the best performing keywords on my clients AdSense also returns them at the top of the organic rankings. Is it good practice to disable this keyword in Google AdWords and allow the organic ranking to do the rest of the work, and subsequently allow the balance to be invested in other keywords?
That figure of doubling comes from Google's reps, so take it with a grain of salt. However, in my experience, it helps you to bid on the terms and pay for traffic even if you are #1 in organic. I've never seen it be twice as good, but it can certainly be 30% better.