Since spells/skills don't run on a 24-hour timer on the MUD like they would in table top, I think it could function the same as Lay On Hands - as long as you have enough mana it will work. I believe the mana cost should be significantly higher, though. Smite Evil is a very powerful weapon in a paladin's arsenal and potentially deadly at high levels. I believe this would be a counterbalance to some of the "insta-death" spells such as Harm (favoured by evil clerics), Distintegrate or Finger of Death. As with some other skills/spells, Smite Evil would only be useable when the paladin has high enough Favour.
For those who don't have the book, here's what I'm talking about
"Smite Evil: Once per day, a paladin of 2nd level or higher may attempt to smite evil with one normal melee attack. She adds her Charisma modifier (if positive) to her attack roll and deals 1 extra point of damage per level. For example, a 13th-level paladin armed with a longsword would deal 1d8+13 points of damage, plus any additional bonuses for high Strength or magical effects that normally would apply. If the paladin accidentally smites a creature that is not evil, the smite has no effect but it is still used up for that day. Smite evil is a supernatural ability."
3rd Edition Players' Handbook, p. 42









