This is a VERy interesting topic, indeed. In the many years of playing (and I'm ashamed to admit this)but there are still several keys that I just don't feel comfortable in for various songs. For example, if somone started singing "Total Praise" in B nat, I'd be totally lost, and have to mentally figure out how to make it work. I guess that's where practice comes into play...(P.S.) B Nat is not one of my fave keys, as well as A nat, D nat, and E nat......Lord Forgive me!