Don’t know if it is obvious but if you’re running Notes 8 against a Domino 8 server, want to see calendar invitations you haven’t responded to (ghosted in the calendar) and you upgraded from a previous version of Notes you must manually enable it in the calendar profile. Do this by opening the calendar profile, go to the “Calendar & To DoDisplayViews”-tab and check “Display new (unprocessed) notices”.
Also it doesn’t appear to work on invitations you received prior to enabling the functionality… Could be that I simply wasn’t patient enough… 🙂