Traditional software procurement practices in any enterprise involve channels which readily lend themselves to gathering statistics about usage (based on procurement, license agreements, the transaction details, etc.). However with Open Source Software (OSS), typically the software enters the enterprise via direct downloads by individuals within the company making it difficult to get a holistic picture of OSS adoption. For the OSS community as well, there isn't much visibility beyond the number of downloads. The Open Source Census is a "global, collaborative project to collect and share quantitative data on the use of open source software in the enterprise."
The project requests that users of OSS register anonymously with the site and download the OSS Discovery (via BitTorrent) scanning software. At the time of registration, the user is also provided with a census code. The OSS Discovery software scans one or more systems and produces a report of the OSS packages discovered on the system. This report can be submitted to the Census website with some optional non-identifiable statistics about the enterprise. The Census collates data across enterprises to produce useful reports about OSS adoption. For example, here's the report of all OSS packages ranked by number of installations. It's no surprise that Firefox is leading the list given the small population and predominance of desktops in the scans.
Please help the OSS community by signing up for the Census and providing information about your OSS usage.