At home, its the iMac (OS X that is). At work its Windows, but I'm usually using X-Windows on it to work on UNIX. I still have my old Windows box (for Masters of Orion II), but I usually am booting into RedHat on it. Even when I was using Windows, I was running mainly XEmacs, Apache, Tomcat, and Perl on it, so the switch back and forth was quick.