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.

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 :)

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