Not sure on how many - LinuxCounter estimates 80,000,000 Linux users currently. It will certainly be interesting to see what happens with the Steam Machines and more coverage of Linux gaming.

In terms of sales of games on Linux - a couple of recent releases saw Linux make up 16 of the sales, but the overall picture is only about 1% including all of the years of Windows and Mac support on Steam. so it will only grow in the long term. May was actually a bad month for Linux due to the release of GTA V which does not support Linux and is clearly a huge game, but previously some big games like the latest Borderlands and Bioshock Infinite had boosted Linux games sales. The trend is that more of the big releases are coming to Linux so I am sure Rockstart will want a slice of the Linux user base at some point.

Is that Linux on the desktop or does this count all hardware Linux is running on?

I am not entirely sure, but I believe the estimate is related to actual users (people using Linux). This is actually extrapolated from percentage share of desktop users on all OS's. It is not going to be completely accurate, but better than a finger in the air. The statistics will be more interesting next year after the official SteamBox is released and we will see what impact that has - I think that will make a lot more people aware, of SteamOS and then when more people realise you can build your own for very little money, that may encourage more people to dabble with their own Linux installations.

The numbers vary, because the Steam survey isn't very accurate, but on Steam alone it is about 800,000-1,000,000 Linux gamers. Add to that the number of people that prefer GOG or Desura over Steam.

Also many Linux users have been running Steam using Wine which presumably gets reported as Windows. I started doing this 5 or 6 years ago to run games on a Linux laptop I had.

I wonder how many games these users have brought since Steam for Linux came out? I myself have 100 and planning to buy more.

How well did that work for you?

It worked surprisingly well 5 years ago - I was playing games like GTA Vice City and Left 4 Dead - both of which were flawless even on a cheap laptop.

More recently since I installed Xubuntu on my main gaming PC, I have successfully played these using Wine:

GTA San Andreas
S.T.A.L.K.E.R. Shadow of Chernobyl
Hitman: Codename 47
Hitman 2: Silent Assassin
TES IV Oblivion
TES V Skyrim
Mass Effect
Terraria

Then some of my games like Civilization V, Metro Last Light, Mount & Blade and The Witcher 2 - they all have native Linux versions.

You know guys, I'm starting to believe that Linux/SteamOS needs some killer games. Something that will make people buy Steam machines or install Linux just to play these games.

They're already completely sold out.

It looks like Valve underestimated the popularity too.

Not really. It was clear from the beginning that this is an early phase with a limited amount of controllers, thought as a kind of beta phase.

Steam machines, sadly, will not contribute to Linux gaming too much. People will certainly not move to Steam OS just because Valve has now made an operating system. Most people will stick with Windows 10 and Steam installed.

I beg to differ. I am a convert - big Windows gamer, but as soon as enough of my games collection was available on Linux via Steam, I jumped at the chance. Friends and colleagues are doing the same. I doubt it is just people I know and this is before the hype is real.

Unlike Windows 10 or other Linux distributions, SteamOS does not want to be an all purpose OS, it is specifically aimed at giving the user a console-like experience on a console-like PC. The fact that it comes pre-installed on a variety of machines aimed at the living room may very well give a large boost in the usage of Linux as gaming platform.

I don't know about you, but I get the impression that many gamers like to spend ages tinkering with settings to get things working faster for their games and with Linux being completely open it should be much easier for them to do just that. I'm guessing somebody who spends ages building their system with all kinds of tweaks would also like to tweak their OS. Have to admit though that's pure conjecture on my part.