Aviation is one of the smaller users of GPS. Trucks use them extensively, and the hundreds of supertankers which thread their way through the thousands of offshore platforms in the GOM rely on GPS. The internet depends on it completely - the timing from GPS signals is essential for timing. There is no other source of nanosecond timing signals, and nanosecond precision is necessary for networks as well as for position calculation. The relativistic effects of lack of gravity and velocity of the GPS satellites has to be accounted for just to calculate your position to within 10 meters, because it's all done with time differences. I doubt it will be well-publicized, because that defeats the purpose. If I know the GPS system will be turned off next week, then I'll plan my attack for the week after. And with nukes, chemicals, or germs, close counts. You don't need GPS precision to deliver those. Anywhere in New York City or any other city will serve the purpose if you just want to create terror.
This whole thing is just a way to make us think something is being done. Actually turning off the GPS system will create more chaos than a terrorist attack. Wolf, Wolf!!!