In Mango, the People Hub has integrated Twitter, Facebook, LinkedIn, Windows Live Messenger, and Outlook into the same space. It is no longer necessary to launch a browser to connect to friends on any of these services. One thing that was difficult about using Facebook prior to the Mango update was that the app showed you were available for chat when the chat menu on your phone was not visible. This, along with several other issues, has been corrected.
Facebook chat is now integrated with the messaging hub. If you set your chat status to online, a complete list of all your online contacts will be displayed. You can even switch back to texting a contact instead of chat because each thread now includes a switching button.