I've been using my Canon 40D for a few months now, and I can safely say that I have been extremely satisfied with the performance of this camera. It has performed without any issue for over 5000 shots now, and I keep finding new ways to use it every day. I'm glad that I made the decision for a smaller than full-frame camera body; I find that I enjoy the 1.6x factor on the lens I use. Of course, this does have an effect on the overall width of any wide angle lens that I use, but I did expect that.
I have noticed dust buildup on the sensor, and since I have not yet purchased a cleaning system, I tend to keep my shots at wide open aperture, to reduce the appearance of dust. I highly recommend to every DSLR user to use a nice clear sky to their advantage and take a shot with the aperture shut as tight as possible. The resulting image, when focused on infinity will bring out all dust particles on the image sensor (well, actually, on the filter over the image sensor assembly!). Here is a result, after months of use, with a zoom lens, which acts like a "dust vacuum":
Take a closer look at the image above to see the dust particles, particularly on the top left side of the image. I will need to investigate the various cleaning systems available to clean DSLR image sensors. But that's a topic for another day.
As I mentioned, the 40D has performed without any problems, but this does not mean that there are not things that I might change to improve this already fabulous camera. My number one complaint has to do with the power button, which I find inconveniently placed, and with the two positions, I find myself a little more confused than anything. My second concern is with the placement of the operation buttons below the LCD screen. I find that the buttons have a tendency to get pushed when the camera is worn on a strap. I think that this could be resolved by returning the buttons to the left side of the LCD. I have also sided with others with regards to the LCD itself. It was nice of Canon to include a 3 inch display, but it would have been nice for them to include a high resolution display. As things stand, Nikon's LCD displays are FAR superior, for the same level of camera. In a future version of this camera model, I expect that this will be changed.
I will continue to use this camera with great pleasure, and will comment on further use in the future. Bye for now, I'm off to take some night pictures!