It sure does make it easier when hiking or out in the woods and you can carry one with a telephoto set-up, while the other one is set-up with a wide angle lens.
It also calms many arguements considering my wife is always by my side while we are taking pictures. This way, we only swap set-ups if one wants a change, and not have to worry about waiting to share a camera.
I told her about the new 40D and the new Mark III and she jsut rolled her eyes and said "Get the thought out of your head, RIGHT NOW!!" Althought she asked me why I havent bought the MP-3 lens that Dalentch uses?