Eventhough the damage is low it doesn't state any duration just that it can't occur more than once every 6 seconds. If this is the case and you can cast it on multiple targets you pretty much lower the damage done to everyone by 500 every 6 seconds.Originally Posted by Fadibo
This is fairly decent given that you can cast it on multiple targets and it stays on forever (read as: 15+ minutes)
Of course the downside is that it can possibly (like all paladin buffs) be dispelled and the number will be extremely low in WotLK at level 80.
I guess it is a nice little thing to put on your tanks though, a 1 minute fight would equal in 5000 damage absorbed, better than nothing.