"Oh, no! A book. Now I must see the trouble skimming it through for clues the mapper placed there.." ^ After far too many FM, this is my reaction. And any random note is enough to destroy any atmosphere built by the map until that point. "Mmh, what I was doing before reading this poem of the fan mission's author about a guard's boots? Oh, right, I need to evade the dangerous zombies patrolling the nearby hall." Clues: can't you use different kind of clues for the different levels of difficulty? This way you can just give them away on normal and hide them in a encyclopedia on expert.