One of the things I hate about using my mage pet is that while it is much better when you are fighting a group of mobs compared to the scout pet, when its target dies but was part of the mob group, you have to send it after the next mob in the group. When I cast a group damage spell and my current target dies, the group spell keeps on casting, still hitting the other mobs. But my pet immediately stops casting, and I have to make sure I have something (or the tank has something) targetted and then send my pet on the attack again. The whole time, the pet's DPS is suffering, especially considering how long the cast times are for the darn pet. Half the time, so much AE has been thrown around by everyone in the group, my mage pet doesn't even get its first spell off when the 2nd mob of the group encounter has been targetted. My pet starts to cast, gets cut off, and I get to rinse/repeat. Since it seems to be more rare to mez something than not mez something, I'm not too worried about my mage pet casting on mobs it is already engaged with. Let the darn pet not break mez on any mob it hasn't been specifically told to attack, but otherwise, let it keep casting on the group encounter it was already involved with.
Shouldn't need to make a macro to X spell for this, besides there are times you might not want a pet to go in etc blah blah blah. It would be nice to have a toggle in line with follow, passive, etc to make it attack your target or turn it off. /shrug
