A research study sponsored by Novell but conducted independently by IDC in February 2009 confirms the continued replacement of UNIX by Linux on servers. This dovetails with but is different from IDC research into quarterly factory server shipments, which show the same trend. (Quarter 4 2008 results concerning factory server shipments are available here but I have not posted about them yet; quarterly 3 2008 results are discussed on this previous IT Investment Research blog post).
IDC likens the movement to the switch from RISC to x86 servers during the early part of this decade and thinks the reason is the same: the economy! But the research points out that cost and/or cost savings is not the only reason IT users acquire new server operating systems. Among the sample used in this research (but see methodology note below), security and application availability ranked higher than ongoing support costs in terms of importance. Acquisition cost -- often the prime reason cited by the open source blogosphere for using Linux -- ranked fifth. Costs are even less important to this group in choosing client operating software. How would you answer those questions?
A complementary summary of the research is available from Novell. It is full of good statistics on general IT budget planning and virtualization as well.
(Note there is one methodology caution that I see: While 97 percent of the 'n' answering IDC's questions uses Windows along with UNIX and/or Linux and other operating software, the survey process appears to exclude the very substantial demographic that uses only Windows as its server operating software. That may be as many as half of you.)