I think people are pretty appreciative of what Humble Bundle really does. "Piracy is almost always a service problem and not a pricing problem". I don't think you really see anyone pirating Humble Bundles much.
I see a few on 1337x, but they're 2+yrs old. Can't find shit on z-library either. I just don't think Humble is a big target for piracy because -- as stated earlier -- they're pretty reasonable.