PostGIS is used by organizations large and small and has garnered a lot of commercial support. Its ease of use, unmatched performance, feature set, scalability, ease of deployment, and ability to integrate in most any environment makes it a no-brainer solution for most GIS work involving high end analytics and integration with other business processes.
These are sites using PostGIS that are publically accessible
This uses pgRouting (which means PostGIS as well), OpenStreetMap
Below we have a list of links to case studies on how it's currently used.
Stay tuned for our next book pgRouting: A Practical Guide with LocatePress due out late 2015.
© Leo Hsu and Regina Obe 2014