The O'Reilly book CouchDB: The Definitive Guide has an example project called 'Sofa', a blog engine with some pretty cool features.
But it was broken for long time. In fact, until now. :D
After I read the CouchDB book, I decided that maybe even better than following along in the book to build the project, I might learn even more by fixing the obviously broken version.
And I was right: I learned easily as much again as I did reading the book, including figuring how to go about debugging couch apps.