I think it's really well done.
It seems to use the standard email notification system but intercepts the messages before they get into the main BlackBerry inbox. You then get a little facebook icon in the alert are on the BlackBerry home screen.
It doesn't have applications it's really about seeing the status of your friends, poking them, writing on walls and exchanging messages with them.
There's been a lot of talk at CTIA Wireless about mobile device applications just focusing on what the mobile user needs. This follows those principles.
When I'm out and about, the most important functionality to me is communication. Zombies, film quizzes and all the other stuff that you do when you're a bit bored is a lot less important.
Actually what this does for me is change facebook into a powerful, realtime, communication service, rather than something I do when I'm looking for a diversion from whatever I'm working on.
Take this thought forward and email is no longer a communication application but it becomes just a transport layer for a richer, contextual communication paradigm. If I want to communicate with my friends I use facebook, for work I use Outlook.
Crazy valuations or not they are shaking things up. I was a little sceptical about facebook before but the more I get familiar with what they're doing and how they're doing it, I'm becoming more and more impressed.
It's also made me want a BlackBerry Curve, the photo tagging feature looked very cool and my trusty old 8707 just 'aint gonna cut it in the new era.
BTW, BlackBerry screenshot created using BBScreenShooter. You have to also download the BlackBerry JDE (90MB+ which you have to register for) but the application worked a treat, very simple.