According to Jaime Rodriguez on Twitter, a client evangelist at Redmond, the Facebook for Windows Phone 7 team is working on a fix for the problems some users have been experiencing with the official Facebook app. Until the fix is cleared and the app updated on the Marketplace, we recommend to continue using built-in integration, albeit slightly less feature rich.
Stay tuned for an announcement as to when the update is available for download!
Update: The update has been released on the Marketplace and is ready to download. Please update when possible to fix the crashing issues present.