MySQL was a relational database that was missing some very important RDBMS features. CouchDB is not a relational database, and the developers know it's not.
What it is Not
A relational database.
A replacement for relational databases.
Obviously, CouchDB is a cool thing for the cool crowd, and doubtlessly many of the cool crowd are going to shoot themselves in the foot by using CouchDB when they should be using a lame boring RDBMS, which they can't bring themselves to do because that would be like wearing a polo shirt with their company's logo on it. That doesn't mean CouchDB is a bad idea. It's just a very sexy idea that will break a lot of hearts.
What it is Not
A relational database. A replacement for relational databases.
(http://couchdb.apache.org/docs/intro.html)
Obviously, CouchDB is a cool thing for the cool crowd, and doubtlessly many of the cool crowd are going to shoot themselves in the foot by using CouchDB when they should be using a lame boring RDBMS, which they can't bring themselves to do because that would be like wearing a polo shirt with their company's logo on it. That doesn't mean CouchDB is a bad idea. It's just a very sexy idea that will break a lot of hearts.