3 little design critiques for some aspiring icon designer to maybe consider:
* I find the current 3D Box icon oddly jarring because uses a "looking-up-from-below" perspective. All the other tools can be interpreted as either being completely flat or as looking down on something (e.g. pencil, pen -- you're never looking up at your pen). It makes it feel to me like I'm jerking my neck up and down as I scan over the tools. I'm sure there's a comment in a Scott McCloud book somewhere about not jerking around the viewpoint like this. :-)
* The gradient icon just read well for me. Being right next to the hierarchy thingy makes it look very much to me like it's some kind of connector gizmo. And having the gradient just be a simple white to green makes it look like it's just a button with cool shading, not a button *about* making cool shading. (The rectangle button has almost identical shading) I think a nonsquare background shape would help (rectangle maybe even) and a three band, or 2-band color->complement (eg orange->blue) gradient in the background would help make it clear that the gradient was the point. Oh and pixel align those handles (like in the pen icon) so they're not all blurry!
* There seems to be a little inconsistency in the design of the shape icons. Rect and 3D Box have a little white inner border inside the black outline. Circle and stars do not. Also I think something more interesting could be done to tie their colors together. Different colors is good, but somehow the current cyan, purple, pink, yellow just don't look like a coherent colorscheme to me. They don't seem to form any sort of progression. Also the rectangle shape feels significantly bigger than the others. Perhaps making it a few pixels smaller and slightly more rectangular would be nice.
I love the pencil / pen / calligraphy / bucket icons. Those have a very unified look and communicate their functions very well.
--bb