Actually, I use Windows/Linux/OS X as needed, but since I deploy and use Linux servers, for quite a while I just used Linux most of the time. That (temporarily?) changed when my publisher (for the Ruby book that I am writing) requested that I use Word and their templates. I usually use OpenOffice.org but since I own Word licenses for Windows and OS X, I gave each a quick try again and decided that Microsoft did a better job writing a word processor for someone else's operating system :-)
In this process, I just updated my trusty old dual 1GHz G4 tower to OS X 10.4 and as much as I am a Linux fan I must admit that for writing, using IntelliJ for Java development, and developing in Ruby, OS X really is more productive than Linux. The OS X X11 support is good, so accessing my Linux servers can be done via X11 or SSH. So, I love Linux, but logic dictates that OS X makes a better development desktop - even when developing web applications to be deployed on Linux.