[yrb]

You could also arge that adopters 'sql style RDBMS' end up building a NoSQL datastore.

If you find you are using a lot of EAV, polymorphic associations, multicolumn attributes, trees, graphs it might be a better option to go down one the on of the many NoSQL routes. Key/Value, Column Stores, Document and Graph databases. Sometimes you can make huge gains in design simplicity because you persistance and/or queries map far more cleanly.

An interesting example of "NoSQL" on top of an "RDBMS" is Salesforce [1].

A huge upside to RDBMS in my view is that they are 'well understood' in production, and operations know how to deal with them.

It is a big design space out there, and you can make a lot of tradeoffs :)

[1] http://www.infoq.com/presentations/SalesForce-Multi-Tenant-A...