I bought a Canon 20D just over 2 years ago and thought it was a brilliant camera. I've never had problems. I saw the 5D come out and didn't see a need to "upgrade" to it. But the new 40D is just something else. I have it about 5 days now and I'm like a child at Christmas.There is just so much to praise about this camera - large LCD screen which is very clear, faster focusing, especially when using centre focus point, larger burst rate - ok, this has now caused me no end of problems, like firing off a burst of 20 images when I really only needed 3, and filling my memory card in no time.This camera is well worth it's price. It's a brilliant step between the 400D and the 1D. I don't have the need (nor money) for the 1D Mk III. This new 40D is just what I need.My first day of shooting with it was at a horse racing event. I was between two other photographers - one using a 30D and the other using a 1D. I felt like mine was capturing just what I wanted and in brilliant clarity. Ok, not the same fps as the 1D, but my friend with his 30D kept looking at me and laughing - it was because he would get 2-3 shots and I was taking about 20.For anyone thinking of this camera - try it out. You will not fail to be impressed. 

Question: What is the size of the camera sensor?
Answer: There is just so much to praise about this camera