"humble tip?"
That is the percentage paid to the Humble Bundle people for putting this together and administering it. While that might seem exorbitant, let me put it into perspective for you, since I was on the inside of this one.
Humble is administering all accounting and payout. This means dividing up the money, paying immediate taxes, filing 1099s for the authors, cutting checks and distributing. This is not inconsiderable work and is the reason why, although I have been the editor of record on SEVERAL anthologies, I have paid an outside packager on all of them to do all of that for me.
Humble did ALL of the reformatting work for us on the books to put them into e-format of three types from .doc files. To give you an idea of just how much work that was, although the signup and coordination on this bundle began six months ago, we were literally right up to the wire on getting all of the files cleaned up and bugs taken out. They ended up having to farm it out to three different entities for the reformatting.
And of course: Humble does the website creation (new page for every new bundle), the store, the art processing, in my case at least creating a brand new cover image from Larry's art, and all of the administration to make this possible.
So....doesn't seem quite so exorbitant now, does it?
