Blue post:

"One thing I can tell you is that chest piece heirlooms will be available in the next content patch. They will provide a 10% experience bonus that stacks with the shoulder bonus. "

http://forums.worldofwarcraft.com/th...34&pageNo=2#36

So 1.1*1.1 = 1.21 = 21% faster leveling - woot - when is "next content patch" - I really need this for my straggler teams