Jane Silber, the boss at Canonical, says that Ubuntu has about 10 million installations and is growing at about 10% per month. That would make Ubuntu the 1% that NetApplications sees. Since there are several distros with similar popularity to Ubuntu, we can conclude that the share of PCs running GNU/Linux is a lot closer to 10% than it is to 1%. Indeed, I installed 135 seats of Ubuntu in a school which just count as a few installations because they are mostly thin clients.
Ubuntu gets more than 2300 hits per day on DistroWatch but Fedora, Mint, OpenSUSE, Mandrive, Debian and PCLinux all get over 1000 each accounting for three times as many hits as Ubuntu. That’s 10000 hits per day for the bunch of them. Multiply by 30 days and I can see how you can get 10% growth per month.
Then there’s LinuxQuestions.org that gets thousands of new members per month. Their logs show a high proportion of GNU/Linux users visiting the site:
What’s with the high proportion of that other OS? Are a lot of folks migrating and installing their own? Great! The diversity and number of ads on the site shows the advertisers like the traffic, too. There are 4 million posts in the forums and 430000 registered members.
I do not know with precision how many installations or users with GNU/Linux exist but it is huge and growing fast. It has been growing fast for years and will continue as far as I can tell. The conditions that caused people to switch are still around: malware, slowing down, re-re-reboots, price and freedom.