There’s been a lot of talk about the fact that resto druids will be sheep-able in Cataclysm. This is due to the fact that they’re not in a shapeshift form, and while shapeshift forms still protect against polymorph, the act of shapeshifting does not break polymorph effects.
Example, Bear Form:
Shapeshift into bear form, increasing melee attack power by 30, armor contribution from cloth and leather items by (cond($lt(level, 40), 65, 120))%, and Stamina by 25%. Causes agility to increase attack power. Also protects the caster from Polymorph effects and allows the use of various bear abilities.
The act of shapeshifting frees the caster of Movement Impairing effects.
(If you’re wondering about the equation in there, it looks like Dire Bear Form was removed, but at level 40, Bear Form gives 120% armor boost instead of 65%, mimicking Dire Bear Form.)
Now, let’s look at Moonkin Form:
Shapeshift into Moonkin Form. While in this form your Arcane and Nature spell damage is increased by 10%, the armor contribution from items is increased by 120%, and grants 5% spell haste to all nearby friendly and raid targets within 100 yards. The Moonkin can not cast healing or resurrection spells while shapeshifted.
The act of shapeshifting frees the caster of Polymorph and Movement Impairing effects.
Why is this good? If for some reason you must leave Moonkin Form to heal yourself, tranquility, etc, you do not need to fear getting sheeped, as you can still break it by shifting into Moonkin Form.
UPDATE: I’ve had a chance to test this and it seems moonkin form currently does not break polymorph.