PostgreSQL/PostGIS is a widely supported opensource RDBMS which is in use in several larger organisations and growing. Functionality, usage and development under PostgreSQL are much cheaper than under Oracle spatial i.e. in my experience. It is often the base of a large geospatial infrastructure. In this position it is a usefull gdi-tool and gets more and more in the focus of smaller and medium organisations and companies, but the support in ArcGIS is very low. Sure, you can inslall the client lib to get read access to a mostly older version of a postgres-server, but if you need a real productive access you have to spend a lot of money for extensions or server installations. For a smaller company this is mostly too expensive and there is not the experience, knowhow and time available to manage a gdi with wfs and wms.
For me, it is not comprehensible why there is at least no support for the most actual postgres-version or a simple read-write access. Every competitor provides this support, i.e. autodesk for free, which is a great opportunity to connect CAD to GIS. Also, the postgres-api does not change this often to limit the acces to a specific version. No client does care about the server version, it just works. So this should not be a great deal to do.
You did this already some time ago with spatialite, which is great for desktop use and data exchange but does not solve larger problems.
