I've used it with rails for a short time now, still trying to dig deeper -- I really don't know if it's more reliable or mature than Mongo, but it was also a relatively pleasant experience. Also, I do know that it integrates very nicely with rails, and that you should use couchrest with it if you're on rails (http://github.com/couchrest/couchrest).

Side comment: learning to write map reduce algos instead of just querying was kind of difficult at first (for document databases in general). The article seems to have neglected to mention it -- it had the steepest learning curve in the overall couch-learning process for me.