JJA4 is right - there will be many answers.
On the Dash 8, we typically de-ice with Flap 15, then reposition to the takeoff flap setting (0, 5, 10, 15 - depending on conditions & supplement applicability) once the spray is complete.
Now, considering the Dash is a high-wing aircraft, there is not the need to worry too much about spray from the wheels hitting the flaps during taxi, but on low wing aircraft I too would consider raising the flaps once the spray was complete (assuming there was no restriction in the AFM).
After landing, I think JJA4 has it spot on - if landing in moderate to heavy icing, leave them where they are until you can inspect the airplane.