A stable alternative to Windows, used primarily on servers and workstations. A favorite of graphic artist, 3D animators, and programmers, as well as corporations that can't afford for their computers to crash. Runs programs such as Alias|Wavefront's Maya, SoftImage's XSI, Adobe Photoshop etc. extremely well, but has trouble running software designed solely for the Windows operating system such as games (duh). In other words, Linux is used mostly by professionals who need a stable platform to do work on, rather than for playing games.
I use Linux on my servers and workstations that are designed for Maya and Photoshop, and I use Windows on my gaming computers.