I've heard that a Pocket Lint is made from these, but it can be the opposite way aswell. Besides getting a copper, what would one of your toons do with these if they could? I was thinking about socketing Thunderfury, but it's too simple. Maybe are they a secret reagent for Perky Blaster?
"Tomb of Immortal Darkness" is not the newest dungeon, it was a 2011 April Fool's joke. Go figure.
Whenever I got one of these, I always just vendored it. They are useless.
The same will be true for the stones that make your pets blue (rare) quality if the ones that make them purple (epic) go live... unless those stones can only be used on pets that are already blue quality.
What I would have done with the green stones if I had been in charge of designing them would have been to make the pet go up one quality rank... so if used on a poor, it would become common, if used on a common, it would be made uncommon, and if used on an uncommon, it would make it rare. That way they would at least have been of some use.
But Blizzard decided that they were useful as they are, and ignored the facts that a) you pretty much need rare quality pets to do pvp pet battles to begin with, and b) the blue stones will work on any quality pet.