It's still a very humbling experience when you've got your new Linux distro running and tuned exactly the way you want it, to realize that thousands of people around the world gave up their personal time to give you a fast, secure, stable & feature-rich OS for free.
How many businesses would not have existed today if it wasn't for Linux, because the Mac & Windows licencing fees simply made it impossible to start your own small business. There would have been no Facebook, Twitter or YouTube. Or next time when you switch on your mobile phone, PS3, ADSL router, desktop, notebook, server, supercomputer, etc and remember that they're all running Linux.
Just think about that.