There is an amazing rant over at Computer World by Stephen J. Vaughan-Nichols that has some really intense data.  When having discussions with people about the penetration of any OS it’s really hard to get good numbers.  In this article Mr. Vaughan-Nichols takes issue with the IDC numbers focused on sales of computers.  I agree with him that sales, especially when trying to compare Windows to Linux Sales, because the I have only once purchased a server with Linux on it.  Even that time I got Windows as a bonus.  That means that for the numbers reported in sales my purchase still counted as Windows servers.  For most of my clients I recommended purchasing the most cost effective server possible.  That normally meant that they purchased servers with Windows on them and we would then just reformat and install Linux on the machine.  In this article he points to a similar example of Weta, the company that made all of the AWESOME Avatar CGI.  They are reported to have used 35,000 cores on 4,000+ HP blades running Ubuntu.  What is interesting about that is that HP doesn’t see any blade servers with Ubuntu installed so each of those machines counted as Windows machines. So the next time you are debating the installed base of Linux with your favorite Windows Geek remind them that your OS is able to be downloaded for FREE.