I'm a proud GNU/Linux gamer with a gaming rig constructed especially for Linux gaming (I sentimentally call it Linus-Tux-Machina).
Until recently, I mostly played free and open source games, but since I recently earned some money (through participating in Google Summer of Code), I find myself buying all Humble Indie Bundles and many of the games on sale on GoG. I have a great respect for open source developers and a great respect for game developers who create quality games, so I Intend to support anyone who has a reasonable approach to game development and distribution (eg. no DRM, multiple OS support, reasonable licenses), I am personally working towards becoming a commercial open source game developer, but right now I'm working on my own graphics engine based on real-time ray tracing, so it might take a while ;)
In any case, my current gaming environment consists of Ubuntu, CrossOver and DosBox, but I'm considering spending some time to learn Gentoo, just for the fun of it. I do have a virtual machine running Windows XP, since some projects in my university are Windows specific, and if necessary I use this VM to run stuff that doesn't run through CrossOver, but I'll get rid of it as soon as I'm done with my studies.
I also recently bough an Android tablet and I already play some Humble Android Bundle games on it. I'm considering installing Ubuntu on it too, but sadly having root access apparently voids warranty... which is strange considering the owner of a machine should always have root access... but whatever. I'll probably root it anyway for the purpose of creating a swap partition since Android has a bad habit of killing apps without asking for permission if I run more than two games at once.
As for GOG, I see three major options:
1. GOG offers full support for all games on all operating systems.
2. GOG offers full support for the most popular operating systems, but if a game offers native binaries for less popular operating systems, or if it can be run through some third party software (eg. Wine, DosBox, scummvm), they sell those games without support. Or rather, users have to rely on the developers and the community for support. In other words GOG dedicates an amount of money/resources for supporting a given OS roughly proportional to the amount of money they can get from the users of this OS.
3. GOG offers full support for the most popular operating systems and nothing else.
The first option is best, but impossible/impractical. The second option is worse, but possible. The third option is the worst.
Apparently, from what I have seen from GOG's responses on this subject, it appears since they can't choose the best option, they choose the worst instead, since anything in between doesn't meet their quality standards. Strange, considering that not offering a service at all is a much worse quality of service than having it available without support.
The good news is, GOG will eventually have to either support Linux, or cease to exist, since someone else will. In any case we will have great distributors of games with Linux support. It's a matter of time. I personally hope GOG chooses the first option, because as much as non-existence has it's advantages, I think GOG deserves better both for promoting DRM freedom and for reasonable prices.