On multi-use trails I personally believe if you're going faster than someone else it's your responsibility to figure out the passing maneuver and it's your fault if there's any collision. If I see walkers with ipods I slow to nearly their speed and pass very casually. There's no need to be in a hurry to blow past people. If you are in a hurry, take the roads. Think of it as great exercise to accelerate back to your preferred speed each time.
+1, especially take the roads, but fortunately my usual roads along MUPS are not bad for cycling.
My cyclists' version of the Golden Rule is
"Do unto the Pedestrians as you would have the Cagers do unto you."