Valve is forging ahead with plans to port its Steam distribution platform over to Linux and has even managed to tweak Left 4 Dead 2 to run faster on a 32-bit Ubuntu system than on a Windows 7 machine, but as far as John Carmack is concerned, the real challenge will be getting Linux users to open their wallets. Carmack, as you know, is the founder and technical director of id Software, and also an open source advocate. He's also a realist.
"Valve announcing Steam Linux support changes things a bit but we have made two forays into the Linux commercial market, most recently with Quake Live client, and that platform just hasn't carried its weight compared to the Mac on there," Carmack said during his keynote at QuakeCon. "It's great that people are enthusiastic about it, but there's just not nearly as many people that are interested in paying for a game on the [Linux] platform and that just seems to be the reality."
Carmack wasn't trying to cast a wet blanket over Valve's plans by any means, and he pointed out that one thing working in favor of Linux is that integrated graphics drivers are getting better, albeit they still have their issues. He praised Intel for being "completely supportive of open source graphics drivers efforts, that they have chipset docs out there," and said if he had the time, he'd work on optimizing them himself.
You can watch the entire keynote on YouTube (skip ahead to the 45min 26sec mark to hear Carmack's comments on Linux).