About a year ago, a SA from a certain three-letter agency who was pretty fluent in technology (our conversation largely centered around Bitcoin) mentioned that iMessage is not end-to-end encryption. That, to his understanding, it was client<-->apple<-->client TLS encryption.
I think I might actually side with the tin-foils on this one. In any case, iMessage isn't a (well-)documented protocols implementation, so I wouldn't rely on it for security.
Edit: Public scrutiny seems to back up the SA's claim [1].
Yeah I was looking for actual message content in there and couldn't spot it. Not saying that Apple isn't misrepresenting, but I couldn't spot proof that your messages are getting sent without encryption.
I think I might actually side with the tin-foils on this one. In any case, iMessage isn't a (well-)documented protocols implementation, so I wouldn't rely on it for security.
Edit: Public scrutiny seems to back up the SA's claim [1].
1. http://imfreedom.org/wiki/IMessage