I am a professional photographer and used both 40D and 60D. I was very happy with my 40D until I had some hands on experience with 60D. I was so amazed how different it was than 40D.
What Positive Features / Advantages Canon EOS 60D has:
The superb feature is the usable ISO, in 40D I tried not to use more than 400 and in very dark situations 800, more ISO would always leave grainy pictures and it always seemed like taken from a cheap camera. The first thing I noticed was ISO in 60D which was awesome in all ways. Even at 1250 ISO my picture was not that grainy. Even if I take pictures in Auto without flash, I still get very decent results. This is the most important difference in my eye. ISO can go till 6400 in Canon 60D than 1600 in 40D. in low light situations when there is no other choice higher ISO can save you.
Higher Megapixels, 18MP vs the 10MP, believe me it matters, specially when your zoom fails to capture a distant image, you can capture it and crop the picture later on, with 10MP the possibilities are lot lesser, with better ISO image quality is also better so even when cropped it gives nice details.
It’s lighter, believe me it makes a difference when you have to carry a camera around for many hours. It’s 755g vs. 822g. Some people say it doesn’t have alloy body as 40D and it’s not that weather sealant however it really doesn’t make a difference. Both bodies seem exactly the same in hands with rubber coating.
High resolution screen, Canon 40D had pathetic screen, so bad to even judge the quality of the image. I always hated it the most in camera, on the other hand Canon 60D is too good, even better than the image itself. Don’t be fooled by the quality of the image you see on the LCD because in real it’s not that good. I don’t know which one is better, the too bad or the too good but so far I feel the too good is better.
Full HD movies, it’s just a WAO, superb. I am amazed how professional the videos are. Why Canon was not offering this feature before. I hate all other cameras without HD movie now. I recently captured fireworks and it was as amazing as I expected. Loving this feature, I have seen the same camera with an external MIC to be used for capturing some graduation ceremonies in some places. You will just need a bigger memory card with Class 6 or more.
As I mentioned above about MIC, 60D offer external MIC jack and you can attach a high quality MIC to capture the moment with high quality sound. 40D doesn’t have anything like this.
Flip-out screen, Canon 60D offers tilting, twisting and flip-out screen that can be rotated any way you want, if you don’t need it or don’t want to get scratched in your bag, close it completely. I use to a lot to capture myself obviously 😉 and to capture images when my tripod is too high or my camera is in titled position. I use remote shutter release with tripod.
RAW image and JPEG together in 60D, I found this feature very useful because it process JPEG in as well as RAW format at the same time. You can also select the size of the JPEG image, small medium or large. I have selected RAW + JPEG Small so I have instant JPEG with my RAW image.
The only thing that 60D lacks is the shooting speed, 40D offers 6.5fps vs 5.3fps in 60D. It’s not a big compromise to make if you consider all the positive features it offers. Its superb and I never would like to go back to 40D again.