Wow...I didn't know some people didn't know about this option. We've had our Horde twinks for a couple of years and we're always skipping down to the neutral auction houses for them...we actually got them when I decided I wanted a pet collection so we bought the snakes, roaches, hamsters, and flying dragon thingies and just bought them for 5 silver. The heirloom items were always connected to your account so you could always send them to your opposite faction toons (I thought).
This is a also a great way to get the [Cat Carrier (Black Tabby)] that drops off Dropped by Alliance Dalaran Spellscribe in Silverpine Forest, or rarely by Alliance Dalaran Shield Guard, Alliance Dalaran Summoner, or Alliance Dalaran Theurgist in Alterac Mountains.