My YouTrack instance won't give any rss to anonymous feed fetchers, even though guest user is allowed and not banned. My guest account has "Read issue" and "Read comment" permissions (Inherited from group "All Users"). But http://my.server.name/charismaRss/issues/xml still gives empty feed for Google Reader bot etc. If I go to login page and hit "login as guest", then rss are shown nicely for that session.
I noticed that youtrack.jetbrains.net works nicely with Google Reader etc. I guess it means that either I removed neccessary privileges for guest account, or JB instance has been tweaked to allow for anonymous feed fetchers.