I chanced to hear a show on NPR this morning (08 Oct 06) called "Sacred Choral Music." The thing that caught my ear was the hostess' comment on "bi-modal choral arrangement." The conductor had the ladies and gents singing in different keys. The song they sang was "The Water Is Wide." That's a well known folk standard on both sides of the pond, but I never knew of before it as a "sacred" song. The hostess didn't say what keys they sang in, but from the sound of it, my guess would be a major-minor pair. I suppose an attentive arranger could easily enough avoid any dissonances. It sounded fine to my humble ear. Anybody ever hear of that kind of singing before.