As the title says, tomorrow, the AH will be closed forever. If you have any items you have been thinking of selling, then last week was the time. But late is better than never. Get rid of all of your old gems asap. The expansion will have better ones and your current ones will become obsolete.
I am up to about 130 million currently off of selling one of my old Skorns for 50 million, and a set piece recipe for 30 million as well (Stalwart defender or something like that).
If you dont have much gold, you may consider buying a bit before the real money AH goes offline. You will need it for enchanting etc.
I think this is a good thing for Diablo. People can get back to playing for upgrades instead of paying for upgrades.