As a software developer, I have used many flavors of UNIX and Windows over the years. UNIX had always my OS of choice. In fact, I run cygwin on every Windows box that I am forced to use.
Running UNIX at home was not very practical until LINUX came along. So I configured my PC at home to dual-boot Windows 98 and LINUX. I was very comfortable with it but my family was not. LINUX desktop environments (KDE and GNOME) were lacking as well as applications to replace Quicken and MS Word.
Up until last year I had only used a Mac two or three times in my life. Last summer I decided to give Mac OS X a try and bought a refurbished PowerBook. So far, it has been a huge success. My family how has a nice desktop and great applications like Quicken and AppleWorks. I have access to the great command line tools of a traditional version of UNIX as well as a first class X Windows server. Mac OS X is a dream come true.