Couchbase is a Document-Oriented NoSQL Database according to the title of their home page: that puts it on-topic, though of course the NoSQL market is more fragmented and more cutting-edge, meaning each DB has it's own niche and the pool of Q&A here may never be big.
It does seem to be related from a technology perspective to CouchDB, though not so closely that they should share a tag. So, how do we get a couchbase tag? All we need is two open questions with the tag. If there is just one, and no follow-up within a few months, the tag will auto-delete (unless someone takes the trouble to write the tag Wiki).
So, please ask (and answer?) some good Couchbase questions on the site :)