This means that we got approval on the US side to bring Jack home! That doesn't mean he can come home yet... See the white checklist of the right hand side of the page. That will let you know what still needs to be done. The main thing we are waiting on right now is his immigration permit from Korea, also known as EP.
But... back to the I600. It took about 5 weeks. It was approved on 10/21. I was worried that I would have to call them after the 6 week mark and hunt down his info to get it approved since others I have talked to had to do that. I guess we were lucky! I am grateful. One more thing off the checklist!