There are three basic categories of social messages:
1) Conventional greeting: In Myspace, the hotspot of social messages are thanks for add for new friend, birthday, holiday, congratulations to graduation, raise, etc. The greeting is similar to Hallmark greeting cards bought in department stores. Users can get fancy and flashy virtual "cards" from lots of image sites.
2) Social grooming: Facebook widgets expand the scope of message beyond conventional greetings. One popular widget "X me" just for sending "Jane chest bumped me". Another "Food fighting" widget delivers non-conventional social message like "Jane threw an icecream to David". Those "non-sense" social signals are subtle but important in social relationships in the way like animal grooming each other.
3) Passive: Facebook invented passive communication or passive social message. When you login into your facebook account, the first page is a news feed about what's going on with your friend, like "Jane and Mark now are friends", "Jane threw an icecream to David with Food Fighting" (Food Fighting is the link to the widget install page).
