The only potential concern I see with smites is that there might well be times when a paladin wants to bless an ally and there are no enemies present--the obvious example is a trap encounter. It might well be beneficial to give the rogue an AC bonus as she tumbles through the slashing pendulum-blades and dodges the spring-loaded spikes to get to the "off" button, but as written there's no way for a paladin to do that if there's nothing for him to smack. Personally, I'd rule that any smite that buffs an ally can be used without an attack, and you just ignore the attack roll and damage portions of the power (e.g. you can give your ally a "smiteless" Shielding Smite, you're just sacrificing the potential to do 2[W] + Strength modifier to an enemy), but that doesn't appear to be an official option. Still, that's minor enough, IMHO.