Measuring the load (Score 1)

I love the idea that by measuring the frequency of the grid you can tell whether there is a surplus or deficit of power and ...

I don't think they (or at least should) use the frequency to measure the load. You can trust the grid to supply an average frequency as specified (50/60 Hz).
Appliances are more resistant to variations in power (read: voltage) than in current or frequencies and the power supply reflects this; the supply voltage in the outlets are usually "far off" the specified value (110/230 V).