Earlier quoted context omitted.
Contrary to popular belief, actually Linux dominates the film industry. http://www.desktoplinux.com/articles/AT5611327583.html
That's a bit skewed by the thousands of machines in render farms that could be running any (free/bundled) Unix. It'll be interesting to see if OSX Server 10.6 gives them a compelling reason to switch.
Smaller FX shops that don't have IT staff are much more likely to consider it, unless they rely on software that isn't available in OSX, like XSI.
Which reminds me, now Houdini is available for OSX (it might still be beta, but it's coming if not here already).