I started out playing in bands and orchestras, where we always worked with the music in front of us--then moved on to folksinging and bands where everything was done from memory. As the years went by, I wished that I'd written out all the memorized stuff. Over the years, you do forget--

Fred McCormick--you are wrong, of course--memorization has nothing to do with understanding, and is not necessary to communicate the deeper truths in music--one could actually make a good case against memorizing music, because it tends to gloss over a lot of the details in a piece.

At any rate, you lose your memory with age, and it helps to keep a notebook for prompting--unless you are one of those (as evidenced in the cruel and miserable Davey Graham thread) who believe that the minute a performer starts to slip, they should be shot, or at least locked away and never seen or heard again.