Buy the tabard and run dungeons as posted above, I think pre-60 dungeons give 4 rep per trash and 63 for boss. I think LK dungeons give full 15 per trash and whatever per boss, I know reg cata dungeons do and I'm pretty you can just wear it in MoP heroics if you use those to cap valor
For mine (Horde side) I wore tabard and ran heroic UP til the mobs all knew me by name. And the stupid mount still didn't drop. Was zero rep to exalted. /grumble at dungeon mount drop curse
They don't drop on my side you buy them from QM once you reach the rep.
Are you referring to Vixie's reply about the mount? Because if so, she is referring to the mount that drops in UP, not the panda mounts, which pretty much everyone knows you buy from the quartermaster....