These are great!
http://blog.wired.com/cultofmac/2007/03/novell_launches.html

I think the second one is the funniest. To get it, you have to understand that Linux lets you choose between many window managers. So, in Linux you can choose the look and feel of your desktop. You can also unload one window manager and load another without rebooting.

With Mac and Windows you don't have any options, you just get what you are given. Sure both Windows and Mac have highly configurable windows managers, but so does Linux. KDE is much more configurable than either, throw in Beryl (A 3d glx rendering layer) and there is no comparison!

So in short, I can install new window managers whenever I want in Linux. For windows, it is Vista for the next 6 years or so.