Valve's Hardware Survey for July 2013 shows an increase in usage for every recorded Linux distribution, with each distribution seeing increases between 7-22%. As every single distribution seems to be increasing in popularity, I interpret this to mean that as time goes on more people are trying gaming on Linux and they are staying with Linux.

Distribution Proportion of users Increase as proportion of total users Relative increase Ubuntu 13.04 64 bit 0.43% +0.03% +7% Ubuntu 12.04.2 LTS 64 bit 0.20% +0.02% +10% Ubuntu 13.04 0.13% +0.01% +8% Ubuntu 12.04.2 LTS 0.11% +0.01% +9% Linux 64 bit 0.10% +0.01% +10% Linux Mint 15 Olivia 64 bit 0.09% +0.02% +22% Total 1.06% +0.10% +9%

Note that due to the precision of data that is provided there are likely to be rounding issues, so the relative result in the right hand column could be +/- a few percent.