Crypanalysis
Use anything with caution! The cryptosystem is only as secure as the host that it's running on.
Apple has been known to leave back doors open in iPhone and iPad systems, and has even patented some of them. Your encrypted data will only be as secure as Apple wants it to be. (Google for Apple's so called "Security Patent" to see just how insecure they can make it for you!)
I wouldn't use any of these devices to store innovative new ideas pre-patent, or top secret government information! Someone somewhere has the ability to access and download anything on your device. As long as there is a transmitter attached to the system which you cannot disable, and memory space which you cannot monitor, there's always the risk of remote compromise by someone somewhere. And since they have the baseband encrypted, there is no way to even detect a compromise!
Currently, they make available location information to law enforcement agencies by 'pinging' the phones. Apple's latest patent will allow for remote collection of 'forensics dumps' which means they can download anything on the phone, and open up all cameras and microphones in order to surreptitiously monitor the environment around the device. There are currently very little restrictions and it doesn't require a court order. That means that someone working for a law enforcement agency can 'ping' the phone without going through proper checks and balances. The potential for abuse is very real!
I personally wouldn't trust anything with a 3G data transmitter for anything important!