hey. sorry... I just went back and read a couple of posts from the same night I originally responded... I think I was in a crabby mood for some reason
My only experience with cinnamon has been my pumpkin ales I have brewed. I know everybody has different thresholds for spice in beverages. I found that 1/2 tsp at the end of the boil and another 1/4 tsp in the keg (along with a few other spices) gives my pumpkin ale enough spice for people to recognize the flavors but not be overwhelmed by it. Overall, I add 2 teaspoons of total spices to a 5 gallon batch. I know it doesn't seem like much, but I'm not looking for a spice bomb. I think you could find recipes with far more spice than that.
Also, you might consider other spices. For some reason, ginger with blueberries sounds better to me than cinnamon with blueberries. You might just try some mixtures in a small bowl to see how the flavors complement each other before adding anything else to the fermentation.