Also...if Facebook takes "messages" and turns them into real e-mail, then that's another huge killer for Google (and Yahoo and MSN). Think of it...markmaunder@facemail.com.
Actually, really, think of this...the 15-year old girl that babysits my children...she'd never have a reason to ever leave Facebook. She can socialize, send e-mail, search the web...
...and when she goes out on the web--with, as you say, intent--then Facebook will know exactly how to monetize that intent.