Using the FeedBurner Awareness API, you can extract the
circulation data for a blog for a given period of time. If you do this for f.i. the last year, you can draw a nice graph
of how your RSS subscribers have progressed over time.
To do this, you need your FeedBurner name, for instance, for my blog the FeedBurner URL is http://feeds.feedburner.com/joostdevalk, and what you need is the last part, which is in bold.
An example graph:
If you want to use this graph on your blog, just include it as an image using the following code:
If somehow this graph isn't working for a feed of which you are sure it's a FeedBurner feed, it could very well be that the Awareness API isn't enabled on this feed. To enable it do the following: