Imho the LookupError "Feed does not exist" should be handled as a 404 Error, since the Client (or Bots) can simple type in a wrong URL and its not djangos fault.

I have a feed at /blog/feeds/latest/ and I get error reports from my server that someone (an evil bot) has accessed something like that: /blog/feeds/latest/chupeta/admin/manda/include_path=http://tugaspeed.info/ooid.txt/

Its not realy a danger, but I get spamed with useless error messages from my server :)