Facebook 5.0 for Windows Phone 8 is not available in the store, this is a major update for the Facebook app on the Windows Phone platform as it brings an UI overhaul, more features. Microsoft has listened to the user feedback from its Facebook for Windows Phone Beat app program and delivered the app features in comparison to the Facebook apps on other platforms.
Skype has released an Android app that is redesigned more like a Metro interface inline with the WP UI, but in this Facebook app Microsoft has redesigned the Facebook app inline with Android and iOS apps. The app is official for Facebook but it is still built by Microsoft and not Facebook.
The latest update brings several new features apart from the UI overhaul, these include improved navigation, support for high-res pictures, post sharing, Facebook Timeline view and more.
This update right now is available for Windows Phone 8 devices only and Microsoft mentions that they are working on an update for Windows Phone 7 and will be released this summer.
Download Facebook for WP8