Some quick questions. Is this being made available only to those who bought a digital version of the Witcher 2 or should I expect to get this for buying the Retail Premium Edition? Also, if I do get this "back-up" copy can I gift it away because I already own the Digital Premium Edition on GOG too?

I think it is being made available to any non-GOG bought version. I don't know about the gifting part, but it is supposed to be the GOG backup of your retail version (i.e. theoretically it isn't supposed to be a second copy that you own but a backup for your retail copy - which is useless for you since you already have the GOG version too). I suppose technically you could make a new account when you register your retail version and give that account to someone or maybe there is a way to give it to someone else's account, but I don't think you're supposed to do that since it isn't supposed to be a second (or in your case third) copy of the game. However, not being a GOG/CDPR member and not having a non-GOG copy, maybe I shouldn't speak for them either. :) Maybe they would be fine with that since you already have the game on GOG. I don't think so, but maybe.

Just feeling a bit jaded over choosing to support them both Retail and on GOG and seeing someone from Steam... getting the same thing I paid extra in support of them for. Gifting it away would be my form of protest.

http://www.gog.com/en/forum/general/conference_announcements/post18
That might be related, the lowest part of that post.

Ah yeah I remember that now ... so it seems like TET at least officially endorses giving the key away to the GOG version if you already have it :)

Open Solicitation: Not really sure what the Witcher 2 is selling for right now but when I get this key I will be very interested in Grimrock and the AC HoMM VI bundle that are all currently on sale right now. So if you want to trade snap them up now while they are on sale and we can trade when I get this key.