Here are a few resources for Couchdb:

* an intro: http://aimee.mychores.co.uk/2008/09/07/post/320

* a use case: http://kore-nordmann.de/blog/couchdb_a_use_case.html

* CouchDB Implementation: http://horicky.blogspot.com/2008/10/couchdb-implementation.h...

* joins in couchdb: http://www.cmlenz.net/archives/2007/10/couchdb-joins

* peepcode: http://peepcode.com/products/couchdb-with-rails