I tend to use functional hacks; hacks with a purpose. Only a handful of hacks that are fun-based exists if anything. My primary interest, however, is templating (and tweaking as peterska2 stated) the forum. For me, hacking is cool and all but it doesn't mean a thing if vB looks anything out-of-box. What catches the eye is the template/style/design; everything else becomes secondary.
Well, sticking to the original subject matter of this thread I've digressed...