I've been using CouchDB since 2009 or so and am pretty impressed by the jsonb functionality built into PostgreSQL (the RDBMS I generally use for everything). I'm building an application with an abstracted "store" and will be running benchmarks against both in the next few weeks but so far, it looks like PostgreSQL might be a bit slower when writing jsonb fields. For this application, the ease of using just PostgreSQL (versus a hybrid PostgreSQL/CouchDB back-end) is well worth that slight penalty.