Pinging under load is usually detonation, or the sound of the shock wave wave from the gas burning too fast. Usually it occurs under abnormally high cylinder pressures caused by a high compression ratio. The compression ratio can increase over time if carbon builds up in the combustion chamber.
Octane is a measurement of how "fast" the gasoline burns, the higher the octane, the slower the burn. Lead used to be used to increase the octane rating (along with lubricating the valve seats). So a higher octane gas will reduce detonation.
Advancing the ignition timing will also cause detonantion, by causing the burning to start early and reach its "peak" too close to TDC of the piston, when the pressure is highest. Most cars have knock sensors that will retard the timing when detonantion is sensed.
The best way to correct detonation (assuming the electronics of the engine management system is OK) is to get rid of the carbon. The best way of doing that is with the liquid cleaners (not spray) that you let the engine suck in while it is idling. The best is available only from GM, called "GM Top Engine Cleaner" and others from, I think, Pennsoil or Castrol. The basic procedure is to find a vacuum line that goes in as close to the throttle body as possible, and stick the opposite end of the line in the can while the car idles (you may have to increase the idle speed due to the diconnected vac line to keep it from stalling). You will fog out about a city block worth of area with smoke, so you may want to do it when there aren't too many neighbors around. The stuff is pretty hard to find (probably because of the smoke issue scaring the manufacturers and retailers), but I know most Jiffy Lube places will do it (don't let them just run the injector cleaner).
You will notice smoother idle and the knock will be gone as soon as your done.
As far as using premium, most oil companies want you to believe that they put their best additive packages only in the premium gas with their advertisements. I remember hearing that this wasn't true and there were threats/suits to make them stop the false advertising. I don't know for sure if they actually do put better stuff in their premium now, but I tend to doubt it.
If you engine does run fine on regular, with out the computer retarding ignition timing to prevent knocking, then you will actually get a little worse gas mileage with premium as it has a slightly lower btu/gal content due to the addition of the octane improvers. But if your computer is consistantlr retarding the ignition timing because of detonation, the timing change will hurt mileage (and power). Unfortunately you can't really tell what the computer is doing without an onboard scan tool.
The only reasons I can see for Ford recommending against premium, is for the slightly higher mileage for thier CAFE averages, and perhaps they feel the octane additives may accelerate corrosion or be detrimental to some of the newer plastic parts they are using, such as the intake plenum. Either way, its a waste of the owners money if they don't need it.
