An interesting thing I came across writing this: the top writers, Bill Oakley and Josh Weinstein, were showrunners for seasons 7 and 8, immediately stepping down after as:

    Oakley and Weinstein stood down as showrunners after 
    season eight because they "didn't want to break [the 
    show]." Oakley said: "We always said we'd never do a 
    joke that we'd done before."