Ghetto hearthing has been removed from the game, at least in the current PTR build of patch 3.1 (source).

Ghetto hearthing can best be described as temporarily grouping with someone, going into an instance and then leaving the group. The effect of leaving the group is that you are hearthed (to where your hearthstone is set) after one minute of not leaving the instance. Players used this technique if they went to a city, needed to get back to another zone (like Shattrath or Dalaran) and their hearthstone was on cooldown.

This was basically a free hearth, granted you could find an instance to make it usable. Orgrimmar is a great example since RFC is located there.

For example, if your hearthstone was set to Dalaran and is currently on CD. You are in Dalaran but need to buy something from the auction house. You could take a portal from Dalaran to Orgrimmar and do what you need to do from there. Now your somewhat “stuck” in Orgrimmar since your hearth is on CD. In order to “ghetto-hearth” and get back to Dalaran, you would need to group with someone (random person, guildy, friend, whatever), run into RFC (which is located in Org) and then leave group. The effect of this is that you would get a message box that pops up that basically tells you to GTFO or be ported to Dalaran.

The new change on the PTR will still port you out of the instance you are in but instead of sending you to the location where your hearthstone is set, you will be ported to the nearest graveyard – leaving you stuck in the zone you didn’t want to be in.