Mists of Pandaria Adds Account-Wide Mounts to Beta

[News Portal]

And just as well too, considering the price of those things. Yes, you can now share mounts right across your account, regardless of which character actually purchased them. Faction-specific mounts are not part of this change, such as gryphons or elekks, but all other purchased mounts are now available to all your characters. Enjoy your new-found mount-related freedom as you hurtle across the plains, mixing and matching your steeds.

Source: PC Gamer

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[Spooler]

never understood mount collection... I can only ride one

[Cyrinno]

Things to collect beyond gear, since gear is so easily to collect what else can you do in wow?

[Da Chucky]

I think a new name might be in order: World of Mountcraft

[Sathias]

I wonder if this includes mounts such as the blue drake from UK

[Novocaine]

So far it includes every mount, including class specific ones like Paladin Chargers and Warlock Dreadsteeds.

[Bluefire]

wonder if that means the 100 mount achive / mount will become unavalible.

[Novocaine]

Don't see why it would, you can't double up on mounts.

[CJGordon]

wonder if that means the 100 mount achive / mount will become unavalible.

Achievements are apparently going to be account wide also, so I don't see why it wouldn't.
Also I logged in to have a look at this new update and I received the 100 mounts achievement and mount for all my characters, even though I only had 36 or so mounts, lols