There was an interview with Dreamworks ( i think that was the Animation house) they use linux for everything.
In engineering CAD and large manufacturing corporations RHEL and SUSE are the two certified distros for running Teamcenter Product Lifecycle Management softare and Siemens NX CAD/CAM/FEA software (up to version 12) it is a smaller market than Windows versions, but probably took the place of the original unix versions prior to 2000