I use so called "cheat-sheets" all the time, this is because I know my limits. I'm likely to freeze in the middle of a line and lose the lyric entirely when I do.
I do not regard preventing this happening as cheating.
I'd be interested to know your answers to the following questions:
1) Do you regard singing from a songsheet as;
a) unprofessional
b) cheating
c) acceptable
2) Do you perform songs yourself
a) No
b) Yes but only with friends
c) Yes but I accompany myself on an instrument
d) Yes I perform unaccompanied songs
Answers by personal message please. I'll post the results if I get sufficient replies to be significant.
AndyG