Linux is growing every day also for desktop usage, but it must be the first choice particularly if you use computer for:
many programmers use Linux to develop applications, particularly about C, C++ and Java programming languages but also scripting languages like Perl and Python.
Linux is the optimal operating system for web sites and web apps development, many CMS recommand the use of this O.S.
Most hacking tools are designed for Linux, there are also specific distros for hacking like Backtrack.
Linux is a very reliable operating system with a robust file system, it’s suitable to be used as file server.
for video-audio streaming using DLNA applications like PS3 Media Server and Twonky Server.