In the Skills tab I see a grey bar for each of the Druid Class Trees and two more for Cloth and Leather Armour Proficiency. (Unlike say cooking, etc, which are mostly blue as my skills develop.) What are these proficiency bars for? Are they place holders for something not developed yet?

The gey bar are skill that permit you to use the skill that they name.

The cloth armor let you equip cloth armor, the same with leather. When you learn the skill to ride a mount it will be also show as a grey bar.

For the balance, feral and restauration bar, in beta I recall to have seen screenshot that was showing that they skill was need pratice to get up, but it have been forgetten (casting spells of the right magic school was most of the time done out a fight condition and generaly seen as unfun (it is my gest)), now they auto increment and probably used to calculate the resist from the mob to the spell/skill that you use on them (hard to test that, I never see an +balance skill item).

I hope that it help.

Eridalafar

Interesting. Maybe they are something not used either yet or anymore. I've had The Cloth and Leather Armor bars since forever and they were grey at level 1 and remain grey. The Class proficiencies, I'm not certain were there from the beginning, but they are grey.

[Edit] I confirmed this on the Blizz boards. Apparently they were used in Beta. The stats integration was dropped from the game but they seem to have forgotten to remove the bars.