I spent some time experimenting with the Buzz APIs this morning - well documented and simple to use. The firehose data will be useful for tracking public social media posts.
I set up Google's example app on my AppEngine account and had fun playing with it. Unfortunately, because of the amount of incoming data, it would only run each day for about 4 or 5 hours before hitting the free resource quota limits. Since this was just for fun, I didn't feel like paying for additional resources.