Pimp my Clojure number crunching

Let's start right in the middle of the story, and play with cosine similarity. I'll tell you why in a few minutes. I assume that most programmers have forgotten their math classes, so "cosine similarity" sounds somewhat grandiose. Quick skimming at Wikipedia might puzzle you even more, but, scrolling down to the definition, you can see that it's just a normalized dot product. I know, I know - now you might wonder what dot product really is. Please read my recent linear algebra Hello World art...