It's not great. It's only good for staunch advocates who refuse to run any other operating system. Linux still isn't good enough for joe sixpack to run it as a daily driver. Until they get joe sixpack on board, it'll forever be a niche product without enough inroads to support a gaming ecosystem.
Developers have had decades to get Linux right on the desktop, and they've failed at every turn. Even distros which did a lot more right than the others still aren't as polished and usable as the alternatives. It's time to get your head out of the sand on this, and start examining the reality. OS X has more of a chance at becoming a capable gaming OS than Linux does, and that's really saying something.
What does the typical joe sixpack need?
Web browsing? That works aside from some newer niche Flash stuff
Word processing? That works for a big majority of cases
Playing Music? No iTunes, but otherwise works.
Games? .... well this is the big one.
For every common usecase there's a fairly generic app you can use to get things done regardless of the OS. Sure there's sometimes warts on Linux, but you get warts on Windows and Mac OS as well. My mother has had trouble with her Mac that take me just as much esoteric googling to figure out as anything on Linux.
But games, well that's been the problem. If you want Joe Sixpack to use your system he needs to be able to run almost every game, since Linux has never had that capability of course it's not going to become big on the desktop.
Now that's changed. Linux can do a lot of games and the major obstacle to Joe Sixpack is gone.
It's still not great (gaming is still a problem outside of Steam), and Linux still lacks the marketing power. But I could really see a lot more casual users coming on board, or even some OEMs coming on board with well configured pre-installed Linux machines, either low-end machines made cheaper by not having the Windows tax and having some crappy OEM apps added, or higher-end machines targeted towards power-users who just want a laptop with an Ubuntu or RHEL system where all the esoteric hardware works.