Worst encounter I ever threw, was a scripted one; two dragons, bigguns at that, attacking the party on a narrow ledge. Try and move out of the line of fire, and you fall off a cliff. Take cover in the main door of the temple, and trigger the trap that does 100 damage; not particularly pleasant, even at 11th level. Took two players down when one triggered the trap, and the other took two breath attacks to the face.