The bigest and most important difference between the 5D and the 20D is the full frame vs. 1.6 lens factor. The other differences are not that important, including the 12.8 megapixel resolution on the 5D and the 2.5" LCD display with tiny focus points viewing (only available when you press info menu and the image is shrinked to one fourth). The shutter on the 5D sounds very different than 20D, probably because it travels double the distance (the sensor is more than double the size of the one on 20D). Then the burst rate on 5D is slower and it does not have a built-in flash. The last "feature" ( no built-in flash) is an indication that 5D is designed mostly with the professional in mind. According to the professional opinion, the on camera flash will make the camera looks like ametuerish.

The most impressive feature about 5D seems to be the extra details on the close-ups from the 5D. Please see image Hard Rock Cafe for the details. You are welcome to compare them with the photos taken with 20D in the following gallery: Fall Colors 2004