This could be big. Google is introducing a new set of social networking tools to Gmail. From media sharing to status updates, Google Buzz let's you use your Gmail contact list as what is essentially a "friend list". This makes it compete with literally every social network out there. From the Official Google Blog:

Google Buzz is a new way to start conversations about the things you find interesting. It's built right into Gmail, so you don't have to peck out an entirely new set of friends from scratch — it just works. If you think about it, there's always been a big social network underlying Gmail.