Don't know if there is another thread about this exact thing, didn't find one at least, sorry if there is.
Anyways, account wide achievements got me thinking;
Lets take the Explore Outlands achievement.
Say you have explored Hellfire Peninsula, Terokkar Forest, Blade's Ege, Shadowmoon Valley, Zangarmarsh and Nagrand on char number 1 and gotten the achievements for them. Okey now, since they are achievements in themselves you basically now have those 6 achievements on every character, right? Then, you have character number 2, which explores Netherstorm. Now, you have explored all you need for the "Explore Outland" achievement, do you get it completed then?
Point being, can you complete meta-achievements by doing one part on char 1, one part on char 2, one part on char 3?
Same goes for the Glory of the X, Battlemaster, World event achievements for example. How do you think this will work?