A number of years ago, while in undergrad, I learned clisp for a college class. Then I used it for a semester writing a game engine for an algorithms class (testing the effects of a-b pruning, etc). Prior to that I started using emacs, but really started customizing it after my exposure to clisp. After that, I had yet another undergrad seminar course, AI, where it (well, scheme), was used extensively.

All in all, recursion always came easily to me, and I think that is probably why I took to the lispy languages so easily. That doesn't mean that I could write anything extensive in them right now - it has been too long :)

Oh, and I do use emacs extensively. Tramp and org-mode, font-lock and other features (*cough* tetris *cough*) make it powerful and consistent enough that I have only had to learn some of the power of vi. Of course, it helps with my choice that the platform we use here does not have VIM and some of the other tools available to it.

emacs vs. vi is, however, a relegious issue, and not being more than sufficient in vi (as compared to proficient :), I will leave my choice as my choice only.

Update: Knowing lisp also made map, foo($_) foreach @bar and other concepts of that type very easy to pick up.