I believe that it is one use each per character that works just like the Paladin's ability to Smite Evil, except without ignoring DR. So the rules will be as follows:
Once per day, the character can call out to the powers of good to aid her in her struggle against evil. As a swift action, the character chooses one target within sight to smite. If the target of smite evil is an outsider with the evil subtype, an evil-aligned dragon, or an undead creature, the bonus to damage on the first successful attack increases to 2 points of damage per level the character possesses.
If the character targets a creature that is not evil, the smite is wasted with no effect.
The smite evil effect remains until the target of the smite is dead or the next time the paladin rests and regains her uses of this ability.
Note that the wording of Powerful Justice seems to indicate that they don't gain the deflection bonus to AC as well, and only deal more damage (2 per character level). So what does this mean?
- Going by the Smite Evil rules this is a gain that stays until the target is dead or the character rests and would regain the ability.
- Yes, but you'll have to spend another charge. No word on what happens when you do this to a character who already has a Smite Evil ready to go.
- I'd say it is subject to the regular use of Smite Evil.
- Given that the rules for Powerful Justice indicate that it only gains the bonus damage, and that this is the only way damage increases, so that is what this particular brand of Smite Evil does.