Personally, I don't like to see people performing with the aid of cheat sheets. I believe that, amateur or professional, if you can't learn a song well enough to perform it without the lyrics, then you shouldn't be performing it. In a lot of cases your audience has paid to see/hear you perform, and I believe that you should try to offer them value for money by giving as polished and professional a performance as possible.

As far as David Bowie using cheat sheets is concerned, I would be more than a little pissed by that. Bob Hope used cheat sheets all throughout his career. I've never liked him either.

Cheers

Bugsy