Facebook just announced their new messaging system which is a blend of email, IM and real time chat.
The new Facebook messaging will use your vanity URL name for the facebook.com email address.
As one of the first platforms to get this new feature, Facebook iPhone app will be updated with full support for this messaging feature.
All the messages including facebook messages, emails, chats will be pushed to the iPhone app making it easy for you to stay in touch. Also, you should be able to view your conversation history seamlessly as threaded messages.
Here is a short video on how this will work
On the contrary, you may also want to check out this Lifehacker post on why you don’t want to switch to Facebook email.
Also, the latest Facebook app update has brought a few more options in the logout menu like the ability to set Privacy settings, etc.

