For June 2014, the overall Linux market-share using this randomly-sampled Steam survey was at 1.20%, an increase over May's 1.13%. Ubuntu 14.04 LTS 64-bit continued gaining ground as did Linux Mint 17 Qiana. The 32-bit Linux distributions continue to be (fortunately) declining.
Overall, the numbers this month aren't much of a surprise with generally seeing 1~1.5% Linux gamers on Steam and there not yet being any compelling reason for Windows gamers to switch to Linux, SteamOS and Steam Machines still being developed, etc.
You can dig through the Steam Survey data yourself at SteamPowered.com.