I brewed a Cinnamon Porter two weeks ago. It just went into bottles.
I added two cinnamon sticks that were chopped in a food processor to primary fermentation. While primary was bubbling away, I put three more sticks into ~2oz whiskey (+ 2oz water) and swirled it daily for 4 days.
I put added the whiskey tincture into secondary for 4 days and the initial results have been promising. The aroma was there but not overpowering and the flavor was in the body of the beer but only if you look for it. I found this to be ideal. The flavor and aroma are there but not to the point that it smells like fireball whiskey.
Keep in mind that that cinnamon upsets yeast, so it may be best to just skip the 2 sticks in primary if you have a delicate beer to work with. I wasn't worried since mine was a porter.
If you're interested, send me a message and I'll update you when I try it on February 13th.
Best of luck!