re: "...Couch just doesn't scale...": I am curious, did you try using the BigCouch project, open source released from Cloudant? I have never used BigCouch on a customer project, but have experimented with it and it is easy to setup and is the scaling architecture that Cloudant uses for their data store as a service business.
Not yet... really, it scales enough for us now. but i've noticed people pick Couch because they think it scales better than, say, MySQL out of the box but the reality is the opposite - you have to pull out the book of scale tricks much earlier w/Couch than w/MySQL.
Also, i really like Couch... so don't take what I am saying here or above as an attack.
