How do you use it?
First, do a search (any search). Then on the right side you will see this box:
Once you go to the reports tab you will see each search you've saved like this:
You can have as many or as few of the search reports expanded at a time. You can also export the data to CSV or Google Docs:
Why is it in beta?
First, this is the first feature we've released while in beta; this isn't a "Google beta." Second, this is the first pass at trying to solve a diverse set of problems. You'll notice we're collecting feedback at the bottom of the feature and we want to reserve the right to radically change it if that's what the feedback suggests.