I'm neither a developer, nor have I loaded 5.0 in beta. Some of my cloud functions started working several weeks ago and all my iBooks disappeared. I didn't sweat it, because my iBooks, with the exception of one book, were all free. If I'd paid for them, I wouldn't have been a happy camper. I still don't know what happened to them, and their disappearance doesn't instill trust in Apple's cloud.
On a related note, my music cloud started working at the same time, and suddenly two songs I'd never purchased appeared among my purchases. It's easy to see them, because I've only ever bought one album from iTunes, and I've never shopped for iTunes music since.
I wonder whether other such oddities have happened to others who haven't done anything to engage Apple's cloud.