I just read an interesting article about using PostgreSQL as a key-value store using the hstore module:
Yes I know you are really happy with your “persistent” Key Value store. But did anybody notice hstore that comes along Postgresql. I find Postgresql to be a really great RDBMS that has been ignored all the time.
Okay, maybe the English in this article isn’t that great, but if you haven’t looked into hstore before it might spark your interest.