It's a good idea to throw the breakers and unplug everything, but keep in mind that it may be *years* before you have electricity from the mains.

The thing I worry about are the nuclear power plants. You can them subcritical pretty quick, but a working reactor is full of radioisotopes than decay at their own pace and give off heat that must be removed lest everything melt. Normally grid power is used in a shutdown to power the cooling pumps with diesel generators as a backup, but if a CME nails the grid *and* the generators then you have a problem.