To add to my previous.
There is no need now ever to forget words or tune. Just record your self on an i pod and put the ear piece in (suitably hidden under long hair)and press play. As you just sing along with yourself you can pause to suit your performance or prompt your self with an introduction.
Eye sight and memory probs solved in one.

I know what you are going to say; the only draw back is that as you get older along with eye sight and memory goes the hair. Theres no hiding place for the wire.