I do my software Dev on Mac OS X. I am a backend systems software engineer working on daemons that run in the background on top of FreeBSD. Mac OS X helps since

I do my software Dev on Mac OS X. I am a backend systems software engineer working on daemons that run in the background on top of FreeBSD. Mac OS X helps since it is so similar to FreeBSD it makes it easy for me to test on my own laptop, and I have access to all of the tools I need to do my job in Terminal, such as mercurial, python, easy to install open source software using MacPorts and whatnot. On Windows I would have to dick around with msys, and cygwin, also I would be vastly less efficient because of having to deal with various inconsistencies and possible issues because the code I just wrote might not compile correctly on a POSIX system.