As mattbw pointed out in a previous writeup, the "cheat sheet" is often an item of masterwork for science and engineering students. Institutions which take particular pride in their students often save these sheets (if the students themselves do not) and display them as class memorabilia. Such displays are ripe for historical anthropology, as they show the various attitudes, modes of thought, and artistic tendancies of the examinees immortalized within.
It is also common for these sheets to be used as effigies for disliked classes or the professors teaching them. After a particularly harsh term, angry students may burn or otherwise mutilate the sheets as a means of obtaining "closure".