Linux vs Windows: What do programmers use.

I was woundering if it is a common theme for most "Pro" programmers to use linux. I mean a book called C;Programming I have was written on linux. So which OS is it that programmers or hackers, per say, use?

C# is the best language, that defaults to Windows, but Mono allows for compiling .NET on Linux.  If you're doing any other old programming language, go with Linux, it's more awesome.