... or, "why you should sell innovation via crappy sketches."
There are a number of elements in Facebook's announcement of Messaging which are familiar to those people who, like me, got excited about Google Wave. However they are not simple to explain, so in both cases (the launch of Messaging and the launch of Wave) you see a reliance on crappy sketches to communicate the ideas. In fact, showing you how it actually looks (the user interface) could complicate their point.
One of the key innovations that Facebook is claiming (although, again, it was inherent in Wave) is the notion of a Social Inbox, ie., a place where your communication with friends and family are separated from the rest of the noise that enters your E-Mail's inbox. Another core idea from Facebook is that "messages" don't need to be defined as E-Mails vs. SMS vs. IMs, etc.. Lets just call them Messages. Nice in theory.
And just like all nifty theories in this space - whether it will work ultimately comes down to the UI. The UI is where it gets complicated, in fact (although of course that's where it's supposed to get easier). I'm not sure whether the UI of Facebook Messages will get this right and that's why they don't show it in their video. Because it confuses things. But I do appreciate one more key commonality between Messages and Wave: they were explained with really simple crappy sketches.
This notion is especially important to the times when IA/UX practioners are trying to sell an idea. Providing detailed, finished-looking wireframes makes your audience feel like the product has already been designed. It makes the project feel too polished. Hence last year's trend of "sketchy wireframes," which I came across in this great post on the Boxes and Arrows blog.
Even though you may have already come up with a wireframe that is pretty close to production-ready (the one on the left), there are skins that you can apply to your wireframe to make it sketchy. And the pervading opinion, at this point, is that this will help you explain and ultimately sell your new idea.