Actually, I think the starkness of Facebook's messaging UI is its greatest strength. If they can somehow make real email as simple as that, abstracting away all

Actually, I think the starkness of Facebook's messaging UI is its greatest strength. If they can somehow make real email as simple as that, abstracting away all the decades-old cruft of email that Gmail only partially abstracts away, it will be quite a formidable entry. Add a script that allows non-technical users to log into their Gmail account and set up a redirect... and things could get very interesting.