I'm lucky, in that relations between the departments are excellent at BBH, and were great at my previous agency too. But I've certainly experienced shops where that isn't the case.
A CD I met yesterday on an awards jury had a very interesting psycho-analytic explanation for inter-departmental tensions: he suggested that Account Handlers and Planners in fact hate Creatives, because unconsciously they are jealous that we can do something they're unable to.
Furthermore, since they are dependent on us to come up with ideas, they also resent us, just as all human beings unconsciously resent anyone they are dependent on.
Got a couch? Climb aboard.