About 10 years ago, 10.58 if you want to get really precise, I took the class CS2135 Programming Language Concepts. I remember being really impressed with a lot of the power and expressiveness of functional programming.
This evening, I was working on a little goofy project, and it turned out that doing it with a closure was the clean and useful way to go. I find it amusing that when I finally got around to using these techniques, it was just kind of a natural thing.
The (half done) code is all over here.