Hi there! Just wanted to share this little bit of info.
In 3.1, there is a trainer-taught recipe to cut a Black Diamond into a uncommon level 70 gem (BC gems). You may then either attempt to sell it on the AH ( I prefer not to) or you can vendor it. They vendor for 25s each. So, as long as you buy them for less than 25s each (They average 5-10s each on my server), you're making gold. While it's not insane money, you are getting a decent catch while AFK. Just be sure to stock up on all the Black Diamonds you can, Pre-3.0.
Good luck!
-Jubhub