A very good introduction! I actually haven't looked much at CouchDB, how is it scalability wise? I first had a look at Cassandra, didn't completely like what I saw so I've been looking more into MongoDB.
Freaky - I've been thinking about doing that too, but I've completed so much already in PHP - maybe when I release a second version of my application. Maybe I should give Django a try.
It's a nice series. What I find hardest in CouchDB is dealing with eventual consistency and conflict resolution (instead of transactions). I wish there were more articles and literature about how to handle that stuff, in various kinds of application scenarios. (Not just documenting how _rev and _conflicts work etc.)