It just doesn't work...
I tried the "Transfer Purchases from [...]'s iPad", both in iTunes 10 and 11. It is HORRIBLY BUGGY. For one thing, Apple doesn't know the difference between "to" and "from". Perhaps they missed that day on Sesame Street. Grover explained it quite clearly! When I look at the transfer panel, it shows that stuff is being copied onto my iPad, which is literally out of space. ARRRRGGGHH!
I have two seasons of Breaking Bad I downloaded on my iPad. My iPad is almost full. I tried three ways of doing this: Transfer Purchases, dragging and dropping, cutting and pasting. None of them work.
Transfer Purchases makes quite a mess. It ended up doubling the tracks on some albums. Now I have a mysterious track on my iPad that is some large GUID number. WTF happened?!?
So the way it will work is the the way that will choke up my internet connection for 40 hours and add $20 to my power bill -- re-download.
It just sucks! I have to say, I like most Apple stuff. I used to use Windows. That said, iTunes is just the buggiest pile of crap I have ever used.
UPDATE: I deleted Season 4 of Breaking Bad (it's on Netflix now anyway) to free up some space on my iPad. It appears to be working now. You just need a lot of free space. So much for that 64GB iPad. I had 5GB of space free when it "just didn't work". Apparently, you need a lot of free space, because Apple doesn't know the difference between "to" and "from". When you transfer purchases "from" your iPad, it actually needs to (temporarily?) sync some stuff over *to* your iPad.
The transfer is dead slow. Try doing it with the cable instead of over wi-fi. The wi-fi transfer is almost as slow as downloading it from iTunes.
It's a bummer. I really wanted to keep Season 4. I paid for it, and it looks better than Netflix streaming. I just don't want to re-download it again. Ugh, Apple, why you gotta be like that?
I wrote up a whole
troubleshooting guide for iTunes wi-fi sync. It has iTunes 10 screenshots, but most of the issues are still the same in iTunes 11.