Many good points made here about a subject near and dear. I've tried to impart this same sense to folks that I have asked to join with me in performance. Alice, I especially agree with the notion that time together working on the material is a big key to being able to develope an understanding of the directions and boundaries of any given artist's performance. I also concur with Dave T. and others that knowing how to be supportive with the abilities you have to offer, however humble, to the point of being almost invisible, so that the focus is on the person leading, is a good philosphy to adopt.