Although there are millions GO Launcher Ex users, GO does not support themers, they just make things inconsistent. Themers must create new package for GO if they want to support GO.
When designing icon style, there is a stuff called icon mask, which help themers to create any awesome ideas. However, the usage of GO Launcher Ex mask is just the reverse of other launchers like ADW, Apex, Holo, Nova, etc. It makes themers feel hard to support compatibility to GO.
Here's my icon theme Ripped Hole Icon Theme, the icon mask works in ADW, Apex, Holo and Nova perfectly, but in GO:
Of course, once my design don't need icon mask, I will go back to support GO Launcher Ex.