I've had a canon Rebel XT for about six months now, and it's served me well. However, I'm starting to feel limited by it. I already own a few lenses that are (a lot) more expensive than the XT was, and I feel like it's time for an upgrade to a semi-pro model. I've heard nothing but good things about the 40D, but at the same time, I don't want to buy one if a new model (50D?) is just about to take its place. Can anyone guide me in this choice? I'm about to start my senior year in college, and very much planning to take a digital photography course; are these reasons enough to upgrade now?