In kind of a blend of Twitter, Facebook, blogging and email, Google Buzz is hoping to become your first choice for social networking across all of your platforms. By linking social updates directly with Gmail, Google Buzz has a headstart on most other platforms because all of your email contacts instantly become friends that you follow and who follow you. There are some privacy concerns because this assumes that your email contacts want to be contacted with greater frequency about whatever you decide to post, but it's a tremendous convenience for those who prefer this email integration to expand their social networking circle.
There's a lot at stake for companies whose focus is on user interactions. Twitter and Facebook are certainly taking notice. This point is made clearly in this Mashable article about the good and the bad about Google Buzz. Google Buzz has become a serious overnight threat based on size alone: 38 million Gmail users in the United States (versus 25 Twitter users worldwide) just became friends with one another using a clean and simple system that will take time away from the attention spent on other platforms. Google Buzz is positioned to become a deafening hum in very short order.