Looks really good. Just a few things off the top of my head you may want to look into:
I was going to say to eliminate the border around the buff window, but then I realized one can probably adjust the transparancy to make it disappear. Other than the purpose of grabbing the window easier, a border on that window seems somewhat unnecessary.
Also the buff window seems to be significantly taller than it needs to be. Fifteen buffs is the limit, which would only be one buff space below your bottom-most buff.
The auto-equip area in the inventory is not displaying the class animation. I've noticed this before with Vert style backgrounds. I'm not sure what it entails, but making it so the class animation can be seen would be a plus.
In the group window it looks like there are % listed for people's pets, is this correct? If so, some people might get confused as to who is who, and if playing a healer, might heal a dying pet thinking it's the player lol. Having just a pet health bar the same size as the player's seems sufficient enough to gauge its health.
That's all I've noticed without loading it up and using it. Overall it's a very nice UI that I think would be popular
