I've tried to tell the that there are Fortune 500 companies running
PHP on Windows and IIS (there are, right?).
Target, Tickmaster, Yahoo, Amazon, and the list goes on and on.
Not too sure about this:
http://uptime.netcraft.com/up/graph?site=amazon.com
http://uptime.netcraft.com/up/graph?site=ticketmaster.com
etc
PHP, possibly, but not on IIS and Windows.
I remember at OSCON a couple years ago they said that amazon and ticketmaster where using PHP. They might just hide it well or they might be using it for smaller applications within the company.