Do any of you ever look through a section of the PHB or some other rulebook and realize you have been doing something completely wrong? It amazes me when this happens with something that is really common--like search checks, for example. We have been going about search checks completely wrong. I was stunned to realize that searching a room that is 5 squares long x 5 squares wide x 2 squares high would take 3 hours if you wanted to take 20--assuming you are searching the walls and ceiling as well as the floor. Yeesh!
Other rules that I've recently discovered we were doing wrong are: you can't ready a charge, you can't charge twice your distance in the surprise round, we've been completely neglecting the fact that, in most cases, creatures can provide cover, a full-round action such as a coup de grace is completed on your turn and not right before your next turn, and several others.
All of these I feel like, "How could I have missed that?" DnD is pretty good at making me feel dumb!