HunchBluntley: I think it's safe to say that, for any game that has an extra "gift to friend" button in addition to the usual "reveal your key" button in the "Keys" tab of your Humble library, giving away the Steam keys has been taken into account by both the devs/publishers and Humble Bundle.
SirPrimalform: It's personal principle though, I see no difference between splitting them up like that and sending my GOGs to a friend. Either way it's casual piracy and it doesn't make a difference to me whether they took it into account or not. If they expect a bit of piracy that doesn't make it ok to do.
And besides they all have a potential use as I jump at the chance to GOG Connect my Humble Bundle games.
I haven't done it either, but, as I said above, the system
explicitly supports it. One doesn't even have to use some workaround: you can download the DRM-free build, then -- whether immediately or many months later -- still very easily give away the unused Steam code via the "Gift to a friend" button, which does not
need to exist. It would probably be fairly simple (I would think) for Humble/the devs/whomever is allowed to decide this stuff over there to remove the option for gifting once a download of the DRM-free version has begun. They don't do that.
Again, we're not talking about them giving access to both a DRM-free build and a client-based download code; we're talking about the fact that they give both
with an explicit option to gift the latter from within one's library after purchase. If they didn't intend for this to happen, then the gift option would only appear before purchase, and would apply to everything within the purchase. But there it is.