You know how brush icons in custom palettes look like the brush category icon, and have no label or other distinguishing features? It's a big pain to me, as I like to have the 5 or 6 brushes I am working with on a palette, and they're often in the same category. Maybe I'm the only person bothered by this, I don't know.
You can actually add custom icons (without the pain of having a category per brush) by exporting the palette to a .pal file, editing that, and re-importing it (the file format is described here).
I was thinking of making a tool to do this. Maybe something where you give it the name of an image file and a .pal file and it puts the image into the specified button on the palette. Would anyone be interested in that?
If so I'd probably make it a windows executable -- or maybe Ruby or Perl so it would run on a Mac, but I don't know how many Painter users could possibly want to paint their own brush items *and* have Ruby installed.