We use leeches a lot up in Wisconsin for Smallmouth. In my experience, leeches seem to work best on slip bobber rigs, or some sort of hook with sliding sinker. Usually, we just straight line them so you don't have to worry about them coming off the hook.

The nice thing about leeches when compared to worms, is, they seem to scare off the smaller panfish, and only the decent size panfish and bass will have the courage to bite them.