I dinged 80 and finally got the Mirror Image, the spell which is supposed to be at par with metamorphosis or exotic pets in coolness. I popped the spell, which summoned 3 copies of myself. They didn't seem to do anything until I hit a monster with a spell. They then fireblasted and ran into melee range with the mob, only to be summarily slaughtered. Oh well, perhaps I just don't know how to use the spell.
Try #2. This time I started with a Frost Nova, and the images fireblasted and started pelting the enemy with frostbolts. So far, so good. But why isn't the mob's health budging? I looked at the combat log, which showed that the mirror images only do about 100 damage per fireblast, and around 250 damage per frostbolt. Er.. what?
Try #3, PvP. An Alliance shadowpriest used Shadow Word: Death to kill one of my mirror images, which aggroed the other two. One of them casted Polymorph: Penguin, and the other.. casted fireblast. Great, they're not only ineffectual, they're also morons.
Try #4, water elemental. Considering that the mirror images seem to use only frostbolts, polymorph and fireblasts, I wanted to see what they would do against a frost-immune mob. Sure enough, after the initial fireblast they didn't cast frostbolt.. instead, they started meleeing the elemental. And not only that, they were doing around 600 damage per glancing blow! They're actually more effective in melee than with spells. I feel bad complaining about my copies meleeing in various quests: the AI was obviously making the most of it's abilities.