I saw a fantastic article today by Roger Grimes about the mythology of computing monocultures; great stuff and right in line with (our opinion on this topic):
And if you think patching Windows is hard, try keeping up with several OSes. I sometimes curse out loud because of all the mailing lists I have to track and all the tools I have to use to make sure my systems are patched. I'm pretty sure that, as the number of platforms increases, the amount of consistent, thorough patching decreases.
So, props to Grimes for using his head and for taking a somewhat controversial position.