I had a few back in school that contained on the knowlege of the universe on a 3x5 card. But there was always the one critical one which about half way thorugh the test I REALLY wished I had put on there.
Yup, yup... and it's interesting, the pointless stupid classes usually made me memorize everything, while real classes - like Calculus - let me bring in the formulas because if you don't know the material, all the cheat sheets in the world won't help.