I don't know if it's been said yet or not but:
1) How to carve cakes - STEP BY STEP w/ DETAILS including what kinds of knives to use, etc.
2) Covering strange shapes w/ fondant - like carved cakes
3) How to get your fondant to work right! Fondant consistencies and how to tell if your fondant is the right consistency - some kind of test
4) Consistencies for frostings like French Buttercream or IMBC - HOW can I make it stiffer?? I'm guessing I can thin either w/ water or milk, but what if I want to make it stiffer??
5) How to make stand-up gumpaste or fondant figures
6) How to make sure your layers are even for stacking - do you use a level? How can you tell before you start stacking if your layers will be crooked? Besides looking at them - b/c they can look fine and then you put that second one on top and presto - crooked!
7) How to cut dowel rods
Oh wait I second the cake painting & airbrushing! (including what equipment to buy and maybe where you can get it in the U.S. & elsewhere)
If anyone has answers to these kinds of things and wants to PM me - please feel free to do so!