Something that I left out in my post: the 2:3 aspect ratio senors are physically larger in both dimensions, especially on the wide end, than other alternative aspect ratio sensors. What I'm getting at is that with our 2:3 sensors you always get more image. his shows up absolutely at the wider dimension: if you want to crop to any other common dimension you can do so by "shrinking" the wider dimension without losing anything in the other dimension.
What this means is that you can crop to just about any aspect ratio and still retain good resolution. When you shoot in 2:3, you can crop to, say, 4:5 by taking a little off of the longest dimension without losing anything from the shortest dimension. his holds true for any common aspect ratio since 2:3 is the "longest" astpect ratio in common use aside from panoramas.
Chauncey, cropping to an alternative aspect ratio always cuts out some of the image, so loses some of the physical resolution, but that is just a fact of life. Whether you do it in your camera or in software is up to you. I personally prefer to do it in software, plus I don't use DPP (which is the only software that would recognize the 1D aspect ratio selection, I believe).