A report from Windows Central indicates that as of this morning there were already more than 67 million installations of Windows 10, which is free to Windows 7 and Windows 8 users. During peaks, Microsoft was reportedly utilizing 15 Tb/s of bandwidth. Simply by the numbers, that's impressive with Windows 10 just launching two days ago.
For reference, Canonical reports that Ubuntu has "over 40 million desktop users" in total -- well short of Mark Shuttleworth's dream of having 200 million users by 2015, which was his goal back in 2011. As another metric, Steam in total (OS X + Windows + Linux gamers) had 125 million active users in total as of earlier this year. In general most numbers we see peg the Linux desktop market-share at less than 2% in total... Right now less than 1% of Steam gamers are running Linux (but it's been almost up to 2% in the past), many web metrics put the Linux browser market-share at around 1.5~1.7% usually, and even PortHub reports Linux with a 1.7% desktop market-share.
While sort of off-topic, current Phoronix reader market-share puts 38.7% of traffic as Linux, 30.7% from Windows, 17.9% from Android, 6.2% from OS X, and 4.7% from iOS... Just tossing all these numbers out there for some interesting discussions this weekend in the forums about how to further drive Linux desktop/gaming, "year of the Linux desktop" jokes, how much impact SteamOS will have in the months ahead, etc.