I've just got back from touring. To answer Steve's question I don't think I saw one single singer use a 'prompt' electronic or otherwise.
I am in two minds about the use of words. Half of me realises that with age, memory fails, the other half says that it's lack of practice, or sheer laziness.
A part of the job of singing is training both voice and memory, much in the same way as an actor. I have been training my memory for 50 years, and to this day I can still recite scripts I learnt as a child, and songs I have never sung. I could probably recite most of Jake Thackray's lyrics. Well hooray for me! I'm supposed to remember the chuffing words because I'm a paid singer. If you are a 'hobby' singer and your memory is failing due to age, and you have been supporting Folk Clubs all of your life, then by all means use a 'prompt'. Anybody else, make the effort to learn the words and see how you get on. In my book it shows respect for your material and your audience. You might surprise yourself!