Ease of use
Just for a nice little example, on my Fujitsu Siemens laptop, Ubuntu installs pretty much by itself, mentions it doesn't have certain drivers and requests that I select which ethernet adapter I wish to use, after which it downloads what little it didn't already have.
Windows XP Pro installs, moans about not recognising my videocard, not recognising my wireless network card, doesn't know what my on-board sound is and lacks the drivers for USB 2.0. Windows does not automatically look those drivers up when I hook up to my LAN, it tries to using the Windows update, but I have yet to find any drivers that I need there.
Total time it took me to get Ubuntu running on my laptop? 4 hours, about 3 and a half of which I could do other things, because the install can run itself once it gets to compiling and installing.
Total time it took me to get Windows XP pro running on my laptop? Slightly over 3 hours. Of that, about 30 minutes were used to install Windows, the other 2 and a half hours were spent beating myself senseless trying to get the right drivers.