Waiting in line is big one, but it IS frustrating when you just have one short question like "where does group tour A-24 meet?" You don't want to wait in a line with someone choosing tours for the entire cruise.
I wish they would have a person for "expeditied answers" - she just stands there. If someone has a "long reply" answer then she asks them to get in line - otherwise, she answers them.
Royal Caribbean on Oasis had a great solution (once again, contradiciting the notion that it is a ship of long lines). At the pursers desk they have people walking the line and asking people what their questions are. That way people with short questions are answered right away.