OK, I've now shot my first 4,000 photos with my new 20D, which is my upgrade from my Digital Rebel 300-D. With my DR I was using the 18-55 kit lens. With my 20D, I bought the Canon 17-40 L wide angel, and the 28-135 IS telephoto.
So now, my serious question is .. what's the significant functional difference?
1. a few more options & knobs, Yes.
2. better, sharper focus, with higher % of sharp focus keepers? not noticable. I'm still getting too many out of focus photos in my normal pace of swift shooting. I don't waste time with meticulous set-up. I would rather capture photos and more subject material.
3. feels more expensive hanging around my neck? Yes.
4. better color, contrast, etc. .. not noticable.
5. more durable? Seems like it, at least on the outside with weight and feel.
6. The Canon name brand logo is actually embossed on the front of the D20, whereas it is only flat on the 300-D.
As I use both new lens's on both cameras, I can say that dumping another $1,200 on new lenses has given me some more latitude and opportunities, but I must also say that the 18-55 kit lens that came with my Digital Rebel is quite remarkable considering the price and that it captures at least 85% of the pictures that I can catch by spending $1,200 more on two more lenses. Of course, there are fine nuances with anything we get used to.
One summary conclusion I can make is significant: adding the 17-40 lens to my digital rebel gave me a significantly better total piece of equipment. When I move that same lens to my 20D, I really don't see much difference.
Another first hand summary difference is that I can say the 300-D is a damn fine camera, and should not be poo-poo'd in favor of dumping more money. I love toys so I don't mind buying them to explore, but when it comes to producing photos, I think I can challenge anyone who has a 20D with my 300-D.
For making good photos, nothing replaces brainstorming ideas, seeking good lighting, interesting subjects, creative angles, exploring and practicing. Ever more gear has diminishing returns.
I would like to hear people argue with me and tell me I don't know what I'm talking about. I don't see a quantum leap forward. Maybe there is a huge difference between the 20D and the 300-D, but if there is, it lies in the 3rd Standard Deviation to the right of a normal bell-shaped curve. LOL.