Wikipedia just posted its web stats. As biased as they are we know the site and its content… so I claim it is reasonably representative of what it represents, shares of visits to Wikipedia.org.
It seems to me that it is clear that other OS is losing share in a big way to small cheap computers. In the same period of time Linux rose from 2.28% to 2.98%, a 30% rise in half a year while that other OS dropped 2.5%, a 3% decline, in half a year. I would bet this trend will continue for at least another year and may well accelerate as tablets keep ramping up.