Which all sounds rather like Postgres. It's harder to use because you have to know what you're doing, and it's not as popular even though it's better on some axes that are significant if you're building something solid.

This is true. I think couchdb tries to be all things to all people rather than just focusing on being a great data store. It's a database like mongo, it's a mobile database like sqlite, you can use it to host apps with couchapp, you can use it as a map-reduce cluster like hadoop, etc. I would rather have just a solid no-sql database that solves that problem. I like couch better than mongo for the reasons I mentioned, but I know couch also has problems and still haven't found a good third option.