It's quite interesting to read nothingmuch' reasons for not using CouchDB. In particular this is a bit of a wake-up call for me:
This means that you have to live with the same limitations of SQL queries (the fact that they are non recursive, so they can't express transitive relationships), but you don't get the freedom to write queries ad hoc and have them execute efficiently (ad hoc views are supported, but there are no general purposes indexes).
I really need to find some time to try out Kiokudb soon.