Edit: I couldnt find the webserver but I assumed it ran on FreeBSD or linux when I went to the "Powered by" graphic.
My opinion is that FreeBSD is one of the most secure of "free" OS's and in most cases more secure than anything M$ (as well as more stable) but I'm a unix bigot to begin with. If you want ease of use and don't mind the occasional attack M$/IIS is the way to go, but if you want Security & Stability then FreeBSD/Linux would be the correct option if your not afraid to learn something new. It can be a hassle to get everything configured and setup the way you want it, but once your done you won't have to touch it, barring any security updates.
