I got the idea for cinnamon in
beef stew when I was in Jordan. I can't remember the name of the dish but, instead of
beef,
lamb was used and it was similar in style and prep as pot roast. It was delicious and I agree 100% with
@phatch, a little goes a very long way.
I've made the dish a few times with both
beef and
lamb and literally a small piece of cinnamon in the cooking liquid is all that's needed and by "small piece", I mean about the size of a pinky finger nail. If powdered cinnamon is used, just dust a wooded spoon with it, tap off the excess and stir the liquid with it.
Also, I find that fennel instead of onions with the cinnamon really gives the stew a great depth of flavor.
Cheers.