I do not have a deep understanding of either ATOM or WebDAV but on the surface they seem to overlap in their publishing capabilities. ATOM's does not extend HTTP but WebDAV's does. On the other hand ATOM uses some less well-supported HTTP verbs anyway, so does this point matter?
The ATOM publishing protocol is generating a lot of enthusiasm, even saving us from the WS-xxx. So are these two protocols distinct? When would one be preferred over the other?
What about content-specific issues, like calendars. CalDAV extends WebDAV. Does ATOM have enough not to be extended like this? Should WebDAV be extended like this?