Each extension on Magento Connect has a ranking called Popularity. Details about how it’s calculated:
The popularity score is a measure of the interest in the Magento Extension on Magento Connect. It is based on the number of times the extension is installed from Connect for free extensions and the number of referrals to the developers site for paid extensions with precautions taken to avoid double counting use of the extension.
Magento recently cleaned up Magento connect, more details on their blog post: Improving our Extension Marketplace
On 13th of April I’ve run an analysis of Magento Connect and here are the results: