Interesting news: GMail is now an OpenSocial container. This is as far as I know the first mail system (I mean real mail, not like Facebook or LinkedIn mails) that exposes itself through social network APIs.
Google did not succeeded in the social network arena with Orkut (except in Brazil), but they have a very successful mail system, and this is where the people's real social network is, automatically created from the conversations you have. Your closest friends however are in your phone's addressbook, and if you have an Android phone, they are automatically available in GMail. Google's strategy it taking shape...
Need to play a bit with it, to see how much of GMail is exposed to the OpenSocial gadgets, and how the activity stream materializes in Gmail.