If you follow publishing at all, you probably know that Hugh Howey dropped a bomb on us yesterday. His friend made a web crawler that trawls through Amazon's rankings and aggregates data. We already knew that you could calculate how many books an author was selling from a ranking, and if the author is self-published, you can get a pretty good idea of what she's making. If she's traditionally published, you also have an idea, although it depends on what she was able to negotiate for her contract.
The data that Hugh's webcrawler is making available has never been available before, and it's fascinating. His initial post is long, but worth every minute if you're interested in the industry - http://authorearnings.com/the-report/
Or, if you want the whole thing with a dollop of Joe Konrath snark - http://jakonrath.blogspot.com/
One thing I noticed - audio books, while only a tiny percentage of overall sales compared to ebooks, are still outselling paper 2 to 1. Huh.