Messaging - security/privacy?

[gladoscc]

I'm curious about does and how apple stores the messages, beyond when they were read.

1) Best: messages deleted once read
2) Messages encrypted with the user's password
3) Messages encrypted with an apple-known key
4) No encryption

Given iCloud and moving between different devices. 1 is unlikely. 2 is still good, but given how apple owns iAd, I'm sure they will want to analyze messages that people send..

If you have used the new messaging in the developer beta, do the messages migrate between different devices logged in the same apple account?

I've submitted a privacy question to apple, but does anyone know about it now?