Initially made a single mount/dismount macro that would dismount if already mounted, and vice versa. Went to mount with one toon on the ground while others were flying, and *splat*. I've since taken dismount out of all mount macros and simply changed the dismount keybind in the WOW interface to fix that.

Started a guild run in H VH with me comprising all 3 DPS. After a few trash group kills taking forever, I realize that I had not tweaked my targetting macros properly to work when not running in my full group mode and my shaman and warlock were not killing a damned thing.

Also running up to a ledge in Fjord and stopping the tank right at very edge. Didn't take into account lag in updates between all the windows. All my toons stopped, except the warlock. He flies off the ledge on his dreadsteed, spins mid-air to face me again, and I swear I could see a tear in his eye as he disappeared from sight.