Is the canon 50d primarily made from plastic or from a magnesium-alloy? I have read things that point in either direction. I wasn't able to find anything on Canon's website either. So, does anyone know what it is made from?
The Canon EOS 50D has a magnesium alloy chassis, as did all of the x0D series up through the 50D. The exterior panels are made from various composite materials, mostly plastic and rubber. This is the same type of construction as the higher end EOS xD series like the 1D, 5D, and 7D. The 1D series has a little more weather sealing, which means the openings for the switches and dials are sealed to higher tolerances. The 60D along with the various Rebels, in contrast, has an aluminum/polycarbonate frame as well as composite exterior surfaces.
Here is a picture of the 50D bare chassis that the rest of the camera is built onto. As you can see, some of the exterior surface of the finished camera is the painted magnesium, but much of it has grips, covers, doors, etc, attached.