Do you people not know how to use your cameras? Not to sound like a jerk or anything but I had a 400D for about 7 months and put about 15000 actuations on it. It took some wonderful pictures, let me tell you. I shoot a lot of sports but also do a lot of portraits, and a lot of random PJ stuff. Anyway, I decided to upgrade to the 40D since Canon was running rebates (though the 40D is still the same price after the "rebates" ended lol) and couldn't be happier. After learning to use most of the features it blows the XTi out of the water. The AF is superb and the frame rate is at the perfect speed for leaving it active while shooting sports and still being able to take single shots (if you have fast enough fingers). So for example, I can shoot a football game and take single shots here and there, capturing "moments" (I don't machine gun with my camera, I find it a waste), but when, say, the ball gets intercepted I can just hold the button down and take a series of the interception at a good frame rate.
As for people saying the 40D is "soft", I don't know what their deal is. I put the 70-200 f/4L on it and shoot wide open and it is tack sharp on the "standard" profile. Same with the tamron 17-50 f/2.8. Here are two example shots straight out of the camera with no post processing applied:
from the 17-50

and the 70-200 wide open at 200mm f/4
Neither of those look soft to me and in fact I have had other photographers ask me "Wow, those are sharp! What camera/lens did you use to take those photos?"
The 40D kicks the 400D's butt, no questions asked. If you know how to use the camera and its features, it really is a no-brainer and is definitely worth the extra money. You will not regret it.
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