A Nonny Mouse, even as a pilot I am with you on this one. Yes, sometimes there are special occasions where you cannot "expedite" but you say so BEFORE accepting such a clearance/instruction.
I can understand sticking to a "normal" taxi speed on taxiways et. especially near hazards etc but, after all, we do actually take off on runways at speeds well in excess of taxi speeds!
The other one which makes my blood pressure rise a bit are those who line up (having received take off clearance) and then proceed to occupy the runway stationary for the next 30 seconds, presumably whilst they administer the last rights. Nothwithstanding "icing" conditions and the requirement for a static run, surely when one takes the runway one should be ready to depart without undue delay?