1. Social graph. Many are not active Facebook users but are keeping the accounts cos all their contacts are there. Facebook has actually helped people found their long loss friends and classmates.
2. Sharing links, picture and video. Facebook is replacing email as a means to share interesting contents. One friend actually visits Facebook just to read those contents posted by friends instead of going to the source such as YouTube. "It is easier". Twitter is an obvious alternative.
3. Facebook is the new Flickr.
4. Games. Hopefully when people think of FarmVille or CityVille they think of Zynga and not Facebook. Zynga should seriously break loose of this eco, build its own currency/credit system and focus on iOS/Android platforms.
5. All-in-one ness. Grandmas and aunties love this. Contacts, photos, video, links, cute apps are all-in-one. But this will mean less and less, as this group of not savvy web users will decrease with time.