First off, kudos on an exeptionally well-designed and executed product - 5.02.05 is working very nicely indeed for my mage, lock and druid equally
I have just about become used to the HUD now, after a confusing start as it was so very new to me
One thing I still find tricky to spot is "tapped" mobs - it's difficult to see those which are grey due to someone else hitting them first, versus those which are simply low level.
I use the "Player/Target" style HUD and have the following suggestions for the right-hand side of the HUD:
1. Colour the health bar grey if the target is tapped
> Instantly obvious indicator that you should pick another target
2. Shape the bar differently depending on the target's standing with you:
i.e.
standard ")" shape for red (aggressive) mobs
"|" shape for yellow (attackable, but do not attack you on sight) mobs
"(" shape for green (friendly, unattackable) mobs
> Instantly obvious if your current target is friendly or a mob to start shooting, when it gets a bit thick in the middle of a 25-man raid, for example