Minor Description
The method FilesetArchetypeCreator.getGeneratedSourcesDirectory() always returns the hardcoded value "target" + File.separator + "generated-sources" + File.separator + "archetype". Thus setting a different value for outputDirectory or ${project.build.directory} doesn't have an effect at all, even though the documentation says so.
This should respect the properties set by the user. I do have a scenario in which I want to create an archetype from a project which shall be deployed in an automatic cycle, and in this case it is not useful to generate the archetype to target/...