According to a Garner, as reported in ComputerWorld, "Unix use remains core in data centers, and while its revenue share is predicted to stay flat for the next five years -- from $16.4 billion this year to $16 billion in 2012 -- Gartner analysts this week said users of major Unix systems from Sun , IBM, and HP have nothing to worry about."
Gartner also expects GNU/Linux to grow from $8.6 billion to $12.2 billion over that same period. If GNU/Linux is really a form of UNIX, that means the UNIX/Linux market will grow to $28.2B by 2012. Windows is expected to grow to $22.2 billion by that same time.
Many GNU/Linux users believe that GNU/Linux usage is under reported in analysts reports as many servers originally shipped with Windows are converted to GNU/Linux servers.