The DOD has been doing this for awhile now. I flew through central Nevada near Wilson Creek a few weeks ago and it shut both of my GPS units down. We were on an IFR flight plan in touch with ATC and you wouldn't believe the ruckus it was creating. There were quite a few very concerned pilots. We just asked for vectors and got it, no big deal. Eventually we left the zone and our gps started working again. My first thought was that there was something wrong with the plane.

Personally, I think the DOD is listening in on ATC frequencies and we are part of the experiment to determine the range of some new kind of jamming device.