One of the things that I felt really strong about from the very beginning is the Favourites feature. We have been through a few iterations of how to do it and it was invented even before Facebook launched the new Groups feature and before Google+ introduced the circles feature.
The idea was that out of your whole Facebook friends, you really may not be close friends with absolutely everybody. So we wanted to have a way to filter all the incoming status updates to only show the most relevant of your contacts. This way you will not miss important updates of your closest friends in a long list of Farmville-Spam.
Managing your favourites has the effect of the News Feed showing updates from your favourite friends in a seperate tab and your phonebook showing also only the list of your close friends in the same tab. We also created another seperate application that combines these two into one simple view.
Another not so straightforward goodie is that you can add any person from your contacts directly onto your homescreen. So your best girlfriend/boyfriend can be added here any you will see their avatar appearing. This gives you direct access to their profile with just one click.
Managing favourites is as simple as going through your contact list and mark people from the options menu.