Barely two months old Ubuntu on Steam has grabbed more than 1 percent market share with almost non-existent marketing push from Canonical From Tech Drive-In:

Here's the quick OS market share drill down:

Windows 8: 8.67%
Windows 7: 69.73%
Windows Vista: 6.02%
Windows XP: 10.05%
Mac OS: 3.56%
Ubuntu: 1.12%

 Ubuntu Grabs 1.12 Percent OS Market Share on Steam, Windows 8 at 8.67 Percent