Sometimes my iPad syncs successfully with my Windows PC through iTunes, and sometimes not. The worst problem has been that at some point during backup and/or sync, which occurs automatically when you plug in the iPad to the PC, iTunes will suddenly say the iPad has only 4 GB of storage, rather than 16 GB, and then it will display an error message saying that there has been a problem and that it cannot continue. Then, when you plug the iPad back in, it will say it will have to restore the iPad. This is worrisome, since it did not successfully finish the backup the last time the iPad was connected, so that something could be lost. The last time this happened, I only lost a few contacts from my iPad contact list, and all the books that I had downloaded to to the iBooks app. Fortunately, I had only downloaded free books, and when I redownloaded them, the iTunes store remembered that I had downloaded them before and didn’t give me a hard time.
Another problem with iTunes is that it is slow. Every time I plug in my iPad, iTunes backs it up and syncs it. Sometimes after this, the iPad icon disappears from the left column, so that you can’t do anything with it, and if you unplug it and plug it in again, it backs up and syncs again, until eventually you get an error.
After three or four backups and syncs today, all my downloaded books are missing from my iPad iBooks app. Re-syncing one more time restored the books again.