[einhverfr]

Well, also there is the issue of highly unstructured data. In LedgerSMB, we put it in PostgreSQL along with highly structured data, and just use key-value modelling. These include things like configuration settings for the database in question and the specifics about what a menu item does. I might migrate some of this to hstore in the future (particular the menus).

There are many shortcomings of this approach but when dealing with highly unstructured data (or basically where the inherent structure is that of key/value pairs) it strikes me as the correct approach, and not different really from using NoSQL, XML, or any other non-relational store.