The provided org.apache.couchdb.plist for launchd contains the flag OnDemand set to true, as well as KeepAlive. OnDemand was deprecated in 10.4 and replaced by KeepAlive which is much more powerful. As a result, launchd will NOT restart CouchDB on Snow Leopard after it has been stopped with launchctl stop org.apache.couchdb, as is stated in the README. A manual start or reboot is needed.
Solution: just remove the OnDemand tag from the plist and all is happy happy again.
As a side note: if on-demand loading is really what's wanted, launchd needs more information. There must be information about which socket launchd should monitor, and keeping that in sync with the port number people choose for couchdb seems just way too much work.