I know, you were really hoping for that extra special upgrade that Zuckerberg has been teasing ever since he admitted that HTML5 was a mistake. This should be a nice little improvement, though. Now, no matter which app you do your Facebook messaging from, whether it's messaging in Facebook, or via Facebook Messenger (confused yet?), you'll be able to see which of your friends is online, whether they're mobile, and even pin select friends that you talk to most to the top of the list.
There is also a new, somewhat familiar look to the threads themselves. Additionally, you can "try texting with Messenger" which is a feature that is only available on some phones it seems.