I've been asked a number of times about the best way to encrypt a Core Data persistent store. The answers I've had to give have always been somewhat kludgey at best. Apparently, with iOS 4, there's a better answer, and I was completely unaware of the change. If you're storing anything remotely secure in Core Data, it's worth a few minutes of your time to read Nick Harris' post.
via Brent Simmon's ranchero.com