These tests have been going on since GPS became available. While they can last up to 45 minutes, most of the time the test lasts less than 5 minutes, and very few people seem to have noticed. Aircraft using GPS have lots of backup systems, including transponders, which are linked to ground radar control systems. To my knowledge the tests are never conducted at night, and most occur in the middle of the day in the middle of the week, times when most boaters are too busy watching the horizon.
Rarely, even in war zones, is there a complete outage of GPS. Granted the accuracy isn't pin-point, but it ain't 20-miles off! Now, I don't know about most folks on this form, but I'm going to avoid war zones and other locations where I would put myself or others in harms way. If you want to sail the Somalia Coast using your sextant, knock yourself out. I'll stick to the sunny shores of the U.S. and countries where sailing is fun--not a life-threatening challenge of everyday life.