In Pathfinder, smite damage adds +paladin level (or 2xpaladin level) to damage when smiting evil. The rules for critical hits say:
"A critical hit means that you roll your damage more than once, with all your usual bonuses, and add the rolls together.... Exception: Precision damage (such as from a rogue's sneak attack class feature) and additional damage dice from speacial weapon qualities (such as flaming) are not multiplied when you score a critical hit." (Pp. 184).
I'm not sure whether smite evil counts as precision damage. Thoughts, rulings?