Anyway, the point is…
…every system is different. Which persistence paradigm is best depends on the project and its requirements and properties. All I want to say is that you shouldn't start with RDBMS and then look for reasons not to use it; at the same time, don't start with Project Voldemort or CouchDB just because they're new and exciting. Approach every project with no preconceptions about what you're going to use; or have "flat text files" as the default choice.