Mozilla aspires to be as public as possible with its data and stats. (See Blog of Metrics) We are trying to do our part with AMO and share information about activity we are seeing on the site. Fligtar has two great posts about site metrics during last week’s Firefox 3 launch and the great work that the AMO editor community has done.
We also encourage add-on authors to publish stats about their add-ons. This can be enabled for AMO-hosted add-ons with a flip of a setting accessible at the bottom of your stats chart.
You can view all public add-on stats such as download and active user counts @ https://addons.mozilla.org/statistics/