That used to be my way of shooting. But being a shallow DOF whore too, once you've got the aperture nailed, it's very easy to balance the shutter speed with a suitable Iso. In reality, it's rare light levels change that drastically.
I was interested to listen to a big name wedding snapper at the photography show discuss the way they shoot. They explained that whilst the ceremony was locked down to manual mode, the minute they race outside for the shot coming out the church, theres a need for P mode to get a quick shot. I was thinking, why not have U1 set up in A with auto ISO...