A computer and its OS is just a tool. I've always felt that you need to use the best tool for the job, and in my case that is a Mac running OS X. When I'm working on UI for Sharepoint or for NewsGator's Social Sites product, it helps me tremendously to be able to code in BBEdit on the Mac side and test in IE6 and IE7 in WinXP running on a VM on top of Parallels. No need to lug a clunky Windows-only laptop around or have to deal with the amazing number of hardware/.DLL issues that a lot of Windows-only laptops come with. I don't hate Windows; I just don't like dealing with the problems that come with running Windows as my primary OS.