My team and myself have worked on our own content repository engine, Valkyrie DBVFS, for years. Recently, I found out there is a reference implementation of JSR170 in the Apache site. The project is called Jackrabbit. Although the functionality is very similar with our design, it is still lacking of the highly secure model we are using.
Apache just released Jackrabbit 1.0 last month. I think it worth to take a quick look on what those opensource guys doing with the JSR.