I've only run into a few problems with the mount quests.\
And most of my problems were do to my UI and the pet bar not showing up when needed.

One of the mount quests (flying a plane around a pit) I was able to park all my slaves on the ledge, and they got full credit for my mains work.

While Im sure Blizzard loves our money, multi-boxers are a very small percentage of the player base in WoW.
Weve almost become a spin-off of the hard-core raiding players who scream there isnt enough raid content.

The new content poses a challenge to usbut (IMHO) part of the fun of multi-boxing is overcoming new challenges as they arise.