I don't think i've ever cheated, maybe taking a mental note of range ruler measurements durring the combat phase to plan my next turn, but I'm not sure if that's cheating, plus I rarely bother.
I have forgoten or misinterpreted some rules. We didn't think crit rolls on asteroids counted at first, and when I haven't used HLCs in a while I've forgoten to change the crit to a hit, but I've also forgotten that HLC reroll can crit, so I guess it's a wash there.