Grew up playing the NA game...
We were pretty young, and impatient to start playing rather than study the rules, so we did all kinds of stupid things when we first started playing.
The first major blunder was treating "looking" as requiring the player to trace out with their finger on the board what squares they were looking at. If you didn't specifically look at it, you didn't see it! So going into a room didn't reveal everything by default. So we would go wandering around through empty rooms, hoping not to see anything bad. UNLESS you ran over a square with a monster or piece of door furniture, then you were forced to back up and place it there. I believe the original EU rules said something about how you could open a door and before going in side, look straight through the door to see just what is in front of it. But we weren't even close!
"Roll one red die for each of his mind points... if a 6 is rolled the spell is broken" we took to mean you roll a red die ONCE and it either has to equal his mind points OR be 6 (before that we thought if it was over your mind points or 6, it was broken). We carried on for awhile before we realized that didn't make sense.
We tried though.. we were like.. maybe what you don't know can't hurt you, so the Wizard is actually more susceptible to spells, while the dumb brute Barbarian doesn't know why you're waving your hands around like you think you're some Jedi or something...
We also tried the "buy infinite helmets" loophole. Well maybe you could bang those helmets into a suit of armor or something...
We had some arguments about the rolling boulder in Kellar's Keep... does it hit the wall and roll BACK again? I raised a big stink the first time I got "Command" used on me, arguing that as a "monster," he couldn't use potions, open doors, drop items, etc. Yes, I used to be a sore loser.
And yes, we had the "unlimited treasure searches" thing active too. Later we changed it to all four can search a room, even after the "quest treasure" in it has been found. Still way too easy to get all the good treasure really quickly and gear everyone up too fast.
When a Hero falls into a pit trap, Zargon mentions that they can search the pit for treasure if they want (as the rules state) and we would then forget and let them search it right then and there, even though they already used up their action...
We came back to the game later as adults, and after careful reading of the rules and such we have been much more strict. The "house rule" of heroic feats using your imagination (and villainous feats for the bad guys) in certain situations was satiated with the discovery of the "Combat Cards." That was the first thing from the community we implemented. Good times...
We never reshuffled the Treasure Card Deck before EACH draw (only at the start of each new quest), but I think we had a debate already about that in another thread. Some play it this way always, others do so. So the "real way" is to re-shuffle the deck when a "bad" card gets returned, and only then, right?