I'm pretty sure that every single Humble Bundle has had the largest average donation come from Linux[0].

On some, the total Linux donations even beat the OS X donations, despite having a fraction of the number of users.

[0] Certainly all the ones I've participated in, which is a lot of them.

Yeah, I don't think this is a fair metric either. If anything, I think it illustrates that Linux users, on average, are more generous than their compatriots. It doesn't say anything about whether Linux is "ready" (for some value of "ready"). That said, as an Arch user, I'd love it if more games were ported to Linux (or developed there first, then ported to other platforms). I dislike having to boot to another OS just to play a game...

However, from a pure market standpoint, the Humble Bundles do point out that there's money out there to be made from Linux gaming. Niche markets can be lucrative, and it's even better if the people in that niche have money they're willing to spend. Whenever I see games on Steam that are multiplatform (that includes Linux), I'll buy them over anything else. But, I think that's also something of a confirmation bias--and the fact that I buy them on principle. (I'm not really an avid gamer, and I don't bother much with AAA titles, either.)

Of course, there is one major downside. The Linux market is relatively small compared to Windows and OSX which brings with it other disadvantages.

On the whole, I think this is a positive development. At least someone in the industry seems to be recognizing the need to embrace platforms beyond Windows or consoles.

Those statistics are pretty useless because you set what platform your contribution goes towards. You could pay 1$ on Linux and set it as Windows.

It would be better if we could see price paid vs. platform the game was downloaded for.