McGrath & C-flat - you are right - there is a disadvantage to cribsheets if they lure you into reading them even when you do remember the words. Sometimes Art's method of just a few words to prompt the memory is a better bet. You can just write down a clue to the bits you might be likely to forget.
I really think its OK to use cribsheets if you are not a professional musician. I am the main wage-earner for our family & so I don't have the time to prepare & memorise enough diverse material well enough to cover all the sessions I go to - and would far rather have a crib-sheet than keep singing the same stuff at every venue. This is mainly because I am a crap guitarist (so my accompaniments are always very simple) and rarely sing a song the same way twice - so there's little point investing huge amounts of time perfecting something that I'm only going to sing a few times.
Please note : the above relates only to the situation of playing/singing in a pub session informally. On a proper stage with a paying audience I reckon there's an obligation to be very well prepared - hintsheet probably OK, but not constantly reading a whole cribsheet.