That's almost solely how I make my gold now. Across 5 servers with Ally and Horde on each. You can do the math on the gold
People wonder why I do it but why pay x stupid price for pets on my home server when I can get them for half the price on another. Or mounts. Or BMAH pets or mounts. Sure, it's a long term strategy but it's paying off.
It's not for the faint hearted, that's for sure. And an eidetic memory helps lol