I'm having major issues with Ibooks too. After IOS 5 update was very slow and my books had disappeared. Managed to get a book loaded and it was very slow. Have been trying to reload all of my books but itunes has been copying them on to ipad during sync but ibooks freezes when opened. I'm now restoring my ipad as other apps are also very slow to respond, I'm not hopeful though as I'mm getting the same messages during sync as yesterday.