Hype or not, I inherited a project that had CouchDB baked into the bones. While I found its disk space usage and its time to reindex large databases frustrating, I did appreciate REST-like queries, how it just saved whatever you wanted and how the map/reduce queries could actually be quite powerful for ETL and reporting (though it took a good while to index every time we had a change). We abandoned replication early on as just too chatty over high latency networks.

I love the CouchApp idea because it's a natural extension of "save whatever you want." As long as we're saving json, why not save static files too? It lets you prototype quickly and, in our case, let us develop and test out specific features for clients by quarantining risky crap code on the fly into one database. I like to think we're beyond that stage, but at the time it was invaluable to keep multiple versions of our app running concurrently.

I have 3 solid years of experience working with CouchDB and in the end I find myself longing for PostgreSQL with one bson column for the unknown or "volatile" attributes. Our data was semi-relational, as I would argue is most data. Meaning there were honest to goodness has-many or belongs-to type queries that could have been simplified and easier to maintain outside the application code.

I know that's just a style, some people would use key-value stores for everything with no validation on anything. If you're not that far gone and you still like freedom then CouchDB might be for you. As for me, I wanted an error from my database if my application code asked for something or tried to store something invalid. But for rapid prototyping for us I don't think we could have gotten a better database.