I've been using CouchDB (and now BigCouch) for about four years and it's both clever and useful. We're storing engineering documents (as attachments) and using map/reduce (CouchDB views) to segment the documents by the metadata stored in the fields. The only downside is that adding a view with trillions of rows can take quite a while.
I'd be happy to take the discussion off-line if you want to get into more depth but I have to wonder if the merger of Memcached and CouchDB happened right as CouchDB would have made a name for itself. Right around that time, I think CouchDB and Mongo were equally well-known.
