Microsoft has released version 2.2 of its Facebook app for Windows Phone. The biggest addition is support for Windows Phone 7.5 (codenamed Mango). While most of the apps that come with Windows Phone were updated with Mango, the Facebook app wasn't, until now.
If you've got the Windows Phone Marketplace live tile pinned to your start screen, you should have already gotten a notice that an update is available. You can download the new version from this link: Facebook for Windows Phone.
Version 2.2 gives you the ability to pin elements such as Messages, Events, the News Feed, and Photos directly onto your homescreen. It also includes tile notifications for events, friend requests, tags, and so on.
Microsoft still doesn't seem to offer an official changelog for its Facebook app. If you know otherwise, please let me know.