I finally got the next item on my must-have list, a second body. I got a used 40D from KEH, which arrived a few days ago. It was marked "bargain" condition, but appears solid. Everything seems to work fine, except two things I've noticed.
First, I fairly regularly get an error saying "Can't read CF card: format the CF card for this camera," or words to that effect. This has popped up 4 or 5 times now in about 8 hours of use. It doesn't always happen at power up, sometimes it's when the camera wakes up after sleeping (when I push the shutter button halfway). If I open the door and push the card, and power back up, it's fine. I'm a little bothered, though: I hate to think of missing a critical shot because of having to go through that.
Second, I've been doing some experimenting with burst mode, which is incredible. The high-speed burst is tremendous: one big plus compared to my 550D. But I almost always get one image where the jpeg is messed up. On the camera, it says "Can't replay." On the computer, it's a mucked-up jpeg. The raw, however, is fine.
Has anyone seen either of these problems? If it's an issue with the processor/ROM, I'm inclined to return it. If the CF card is mechanical, and the burst mode is "that's the way it is," I'll probably keep it.
No worthwhile images yet: I'm just playing and learning the controls. I like the control wheel, and love the sound of the shutter. One thing I dislike is that you have to push the "info" button over and over to get settings displayed on the LCD. Every time it goes to sleep or something changes, you have to hit it again. I love the top panel, but the big display on the back is easier to read.