Most of the high-end VFX/CG industry uses Linux for both workstations and render farm nodes. Some studios like Pixar allow a bit more flexibility to some artists in certain roles (generally those that don't work in the pipeline that much - i.e. concept artists) to use other software / OSs, but otherwise it's mostly Linux.

Smaller studios use Windows/Mac a bit more (boutiques use Macs the most), but the removal of the Xserve and the lack of competitiveness in the MacPro for several years have shifted some away from Mac.