We have used Couchbase Server in our product. Its an Intranet application whose front end is pure JavaScript. We however use Erlang/OTP for the Business Logic, authentication (<
Couchbase doesn't have any plans to release an erlang client in the near term. We use Erlang in our product and really like Erlang, but don't have time to put together an Erlang client at the moment. If you are interested in developing an Erlang client we are certainly happy to help and will answer any questions you might have. If you send me an email (see my profile) I will help get you in contact with someone at Couchbase who can help answer questions and get you started on development.
Also, I am not an Erlang user so I am unable to answer any of your questions related to memcached Erlang libraries. Hopefully someone who has can help you.