I'm aware of cedar's alleopathic qualities.
I was listening to a Paul-cast with Geoff Lawton, I forget which number it was, but Geoff mentioned that it took more microbes to digest the wood. More microbes, the better is my understanding.
I do not put cedar in the middle, outside or top of my beds. Strictly in the trench I dug for sod, top soil. The cedar gets as much contact with the ground as possible, to be buried under birch trunks. The cedar is out of touch with any plants, roots (I build big beds). In the long run, i believe I'm adding more microbial diversity to my beds without adding harmful qualities. Plus I'm filling the trenches with water soaked wood, so I don't need to bury as much birch (higher beds, more surface area to grow).
Don't overlook cedar when raising big beds.