I have a 7D and 2 40D and rarely choose the 40's if I am going to shoot with just 1 body.
The way it handles and feels IS a part of the process for me and knowing that the AF is so much better has helped a lot.
On the other hand the 40D is such a deal right now for its capabilities that I have no problem carrying one for any job without an issue.
Shooting interiors I usually have the 40D with 10-22 and I love the combo too.