Investigated the grand parent's question myself, though not extensively. The stackoverflow comment contains a lot of items which aren't true (couchbase does have document id's). The replication is multi-master but is cluster wide, which means couchbase has really nice tools to manage adding/removing nodes but doesn't offer ad-hoc replication (AFAIK). The SO comment also lists a bunch of things which won't matter to many devs like pure http-rest api as they'll end up using client libraries anyway from a middle tier layer.
Not to say Couchdb doesn't have many great advantages like the rest api and self-hosted apps, couchbase does to my mind seem like a good but not 100% alternative to couchdb (and vice-versa). Mainly I like that incremental map reduce is still available along with the atomic type of documents and revisions but clustering is still much more developed in CB.