Summary: I purchased my 40D after taking many other dSLR's into consideration. I compared the Canon EOS 40D to the Nikon D80, D300, and the Canon Rebel XSi. What first got my attention with the XSi is the weight. It was very light which would make it ideal for day-to-day and travel use. Then came the problem. I already owned two L series lenses, so my immediate though was that if I put a heavy, well built lens on a light, entry level camera, it would be heavily front weighted and over balanced.
Then came the problem with the Nikon's. First off, I brought the Nikon D80 into consideration because two of my family members already had it and so I've been able to use the camera quite extensively. Although the Nikon D80 was a great camera, I wanted a more professional one, which led me to the D300 [at the time, the D700 was not available]. I went to the store and tried it out. Overall it felt excellent to hold and had very customizable features. The problem with all Nikon's for me was that I had already invested in lenses, filters, a flash, and multiple other accessories, for my previous Canon camera. So then, I was led to the Canon EOS 40D.
Overall I liked that the 40D was a professional camera though wasn't as heavy as the 1D Mark series. It was more functional in the way that it had a built in flash just in case the camera settings alone couldn't get the light setting the way I wanted, it has a large 3.0in LCD which is great for reviewing photos, and being used with the Liveview function, and it's easier to carry around since it doesn't have a vertical grip [optional accessory].
One of the biggest features that made me go with the 40D was the fps (frames per second) burst rate. At 6.5fps, it easily doubled the 3fps offered by the Nikon D80. This was important to me in capturing sports shots, or fast moving everyday shots. I personally always shoot with my camera in Manual mode (i.e. P, Tv [shutter priority], Av [aperture priority], or M [manual]), so being able to take a shot at 1/8000 shutter speed, makes it almost impossible to get a blurry shot (especially when paired with a IS [image stabilized] lens). Along with a very comfortable view finder, it also supports the Liveview function which, when enabled, allows you to frame your photo on the LCD (more like a compact point and shoot), rather that putting your eye up to the camera. This is great if you need to hold the camera above your head or close the the ground. The only downside is that you have to use manual focus when in the Liveview mode. If you're likely to just put the camera on an auto setting and never bother trying to adjust the setting yourself, and don't plan to purchase any L series lenses, or external flashes, I recommend just getting a Rebel Series camera. Its geared toward being a consumer/ beginner camera and easier to carry around given its light weight.
I purchased the Camera with the Kit lens for a few reasons. First, I already own the EF 16-35mm f/2.8L II USM, and EF 135mm f/2L USM lenses and needed a lens that could cover the area between 35mm and 135mm. Next, the EF 28-135mm f/3.5-5.6 IS USM lens that comes with the camera is light, image stabilized, and great for use as an everyday, walk around lens. It takes great pictures; everything for wide angle group/ landscape pictures, to up-close portrait pictures, and is ideal for almost any situation in between. The only problem that I have, no matter which lens I use, happens in low light conditions. When I take photos outside at night or in a poorly lit room, the camera will take a little longer to focus, and sometimes it would focus unless it has something white or something bright in front of it. Usually this isn't much of a problem though it can be a bother when you have to go to an extremely low shutter speed, use the camera in manual focus, and hold it very steady; or you have to use the flash which allows you to use a very fast shutter speed, though it can make for a washed out shot, and sometimes, using a flash isn't even an option.
Overall, the Canon EOS 40D is one of the best day-to-day cameras I've used. Its easy to carry around, feels very solid, very customizable, and is ideal for any situation. Combined with the fast fps burst rate, liveview, the large LCD, the resolution, the build quality and more, the Canon EOS 40D has the features of the professional dSLR that it is, though the compactness that allows it to be used on-the-go, in the studio, or in any situation in between.
