It's also very easy to add ad-hoc functionality directly from the editor. You can start with a keyboard macro (F3, do crap, F3, do crap, F4, hit F4 again to do "do crap" as many times as you want) and go all the way up to writin elisp packages. M-x find-function makes it easy to look at the internals of whatever library you're using. defadvice makes it easy to do horrible, but expedient, things and get on with your life. IMHO, if you're not writing at least a little bit of elisp, you're not taking advantage of Emacs's real potential.