@eli In the sense you can derive all math from Lambda Calculus, yes, sorta, but in practice: Functional programming is about calling recursive functions instead of control structures. Most Scheme/LISP code has "side effects" (which means it's doing useful work).
@mdhughes you are totally right -- I am a dork for functional programming (weird for someone who, until very recently, wrote mostly PHP). What I appriciated about this article, though, is that she doesn't get bogged down in a specific language's features. I think that the author does a really solid job explaining the core concept of functional programmnig in a conscise way.