Since upgrading to app-engine-patch 1.0 you have to run manage.py instead of the dev server.  However, I hadn’t bothered to trace down why the –datastore_path=filename.datastore parameter wasn’t working until today.

For informal parameters, the name and values are not added separately.  So you can work around this by dropping the ‘=’ between –datastore_path and –history_path.  Otherwise the datastore is put in /tmp on OSX and that gets erased when you reboot.