• It's Free. Both senses, gratis and liberty.
  • It's generally secure by default. Based on Unix concepts, it was designed from the ground up for a multi-user networked environment. Desktop users can't accidentally or deliberately remove or change system files, and viruses targetting the linux desktop are almost unheard of. (Of course, any badly administrated system is susceptible to attack.)
  • You can have a user friendly desktop environment. Although people often complain about them, recent versions of both KDE and GNOME are roughly on par with the MicrosoftWindows GUI.
  • You learn lots. Linux allows you to edit, change and hack away at more options than any other OperatingSystem. Learning to do this increases your understanding of what exactly an OperatingSystem does, and how it interacts with your hardware and software.
  • You will always be able to get support. If you have the SourceCode, you will always be able to pay someone to make changes for you, even if you have 20 year old software. Read Re:I don't pity them for a reason why this is important.
  • For some users, it is very important to know exactly what the OperatingSystem is doing. With OpenSource, you can check the code yourself, provided you have the necessary expertise. With ClosedSource, you need to trust the vendor. This is the reason why several military forces rely on Linux rather than some commercial OS for critical functions.

See also IssuesWithWindows (AsSeenOnSlashdot) and WellThoughtOutReasonsToRunWindows.