I used NetApplications‘ data to create this gem:
It clearly shows that there was a huge migration to GNU/Linux in 2010 in Mountain View, California. Besides showing that Google did migrate users of those other operating systems to GNU/Linux, it shows how NetApplications manages to show GNU/Linux having a minor share globally. The graph above shows some trials or people migrating at home followed by a huge shift at work and a continued upward trend as people did at home what they did at work. Since Google only has 10K employees in Mountain View, they alone could not have caused this shift, unless NetApplications is over-counting them by sampling/counting mostly during business hours.
Mountain View has 74K residents. Google had allowed employees free choice of OS until the summer of 2010. Since business is terribly locked-in to M$’s office suite, sampling during business hours globally may well under-count usage of GNU/Linux.