Originally Posted by
Rivin
Meta achievements are account-level only, so you can acquire the achievements that count for them on any character and they all count towards the meta. So, for Loremaster, you could do Loremaster of Eastern Kingdoms on one character and Loremaster of Kalimdor on another character and they'd both count towards Loremaster itself.
Most non-meta achievements don't count progress from multiple characters, though. Assuming I'm reading it right, WoWDB doesn't show Do A Barrel Roll as having account-wide progress. Neither does Insane in the Membrane (although the title itself should be account-wide once you earn it).