At the moment you can “follow” figures and view a feed of the ones you follow in reverse-chronological order by the time of the latest update (I’m working on an “email me when this changes” option too), and you can drag the thumbnail graphs over one another and drop them to see two numbers compared. The comparison view also gives the option to make your own charts derived from existing ones: e.g., you can make a “per capita” chart by dragging anything over the Census figures and clicking “Proportion.” The “downstream” chart will automatically update when its “upstream” charts do.
It’s very much a work in progress, and if it proves useful, I’d love to hear more from you about the kinds of things that would be of interest to add to it!