Whats the official word on this?
"Soon".

http://forums.worldofwarcraft.com/th...709104&sid=1#0
Let's say we have Account A with a level 70 character, Account B with a level 1 character and Account C with another level 1 character, all three characters are grouped. Account B and Account C are linked, will they receive triple experience?

A: Bonus experience should only be granted if the experience is not trivial to anyone in the group. Our Quality Assurance Team is looking into reports that some of these restrictions are not consistent and hope to resolve the issue soon.