209 No Content vs. application/empty

Mark Nottingham has suggested that rather than inventing a new Accept
header and 209 No Content response type, it might be better to create a
new media type that indicates the absense of content and use Accept to
indicate the preference.  For instance:

In the request:

  Accept: application/empty, application/atom+xml;q=0.5

In the response:

  HTTP 200 OK
  Content-Type: application/empty
  ...

Seems to address the problem quite nicely.  I still think that there is
benefit to the Prefer header but in this particular case, Marks
suggestion seems to be a whole lot easier :-).

- James