Scott, I heard B.B. King do it one time and have loved it since. What's amazing to me is that I can do this song for ANY audience, from Country to Big Band, and it always goes over. It transcends genre.
What a thrill it must have been for you to work with Joe Williams. Some of my best memories have come from sit-ins or shows with some really big names. I'm not much of a hero-worshipper, but the stars are just people like us who have had a little more luck musically. (Or maybe a little more talent?!)
To have a celebrated musician even accept an offer to sit in with me more than validates the respect issue we are discussing under the other string. They wouldn't get up there if it didn't sound good.