It is not obvious that the acorns are actually disclosure arrows – they look like just list bullets. I think using the standard triangle shapes would be better. Or perhaps acorns in the shape of triangles, and pointing right or down like disclosure arrows.

i didn't even notice the acorns until you mentioned it. don't sacrifice usability for better looks.

Drilling down to some categories yields some with no results. (Maybe grey out and don't provide a click-thru to the category if it has no items..)

Thanks for the usability comments guys, I'll switch the acorns to something a bit more obvious :)