I got Google Buzz last night in my gmail account and have started to play around with it a bit.  Here are some initial thoughts.

First off, I agree with Andrew that the integration of Buzz with Gmail will turn out to be a net positive for adoption at least initially (and if it takes off there is always a way to make it available standalone).

Second, this roll out at scale is a very clear example of Google’s impressive infrastructure and how it enables innovation.  Buzz is a big service with lots of features (e.g., likes, comments, payloads and private groups) and yet google is capable of making it available to its large global user base.

Third, it is another example of Google’s willingness to have potentially competing products/services move forward in parallel (here Wave and Buzz).  Some people have seen this as a weakness, e.g. in complaints that there is no “roadmap."  I instead see this as a strength and mentioned that when Google announced Chrome OS (which has significant overlap and potential to compete with Android).

Fourth, Google is already doing some interesting things on the Buzz API side, both with how it is making updates from Buzz available (including PubSubHubbub notifications) and how information can get into Buzz (with apparently more programmatic access coming soon).  This approach based on emerging standards is appealing.

Overall, it is way too early to tell whether Google Buzz will succeed, but I for one am impressed by this launch.