I use Autohotkey for my custom layout. Particularly, I LOVE adding extra modifiers, to add extra layers so that I don't have to move my hands as much, but rather have everything (or as much as possible) within finger reach at the press of a particular modifier.
HOWEVER, I have NOT been able to remap the Fn key for my BlackWidow, or even use it as a modifier, because for some reason Autohotkey doesn't detect it (as far as Autohotkey is concerned, when you press it it sends no input). Apparently, (for some?) keyboards it operates at a level too for autohotkey to work with. I'm also interested in a workaround for this!