1. It's non-proprietary and access is available to virtually anyone
2. It's open-source, so you can tinker with the code
3. Lower cost of ownership
4. Works well with older machines
5. You can customize it to fit your needs. (In Windows, it's hard to remove IE or Media Player from the OS)
6. It's available for many platforms (Mac, x86, Sparc, Alpha, x86-64)
That should be a pretty good start.
You didn't mention anything about specifying the cons, so I won't either.