Re: the title of this post - there are some threats you just can't do anything about, so you try not to worry about them too much, and get on protecting yourself against the ones you can. To that end, I recently participated in a short article on Electro Magnetic Pulse (EMP) risks to the grid and Smart Grid on earth2tech. For background on this topic, here's the Wikipedia entry.
Basically, we should not let EMP concerns sidetrack the good work being done to rapidly advance the state of the Smart Grid. For example, I watched as an EMP discussion temporarily paralyzed a NIST Smart Grid standards working group session for almost half an hour. Don't get me wrong, EMP is a serious topic not to be taken lightly, but standards, no matter how thoughtful and excellent, aren't going to help us much there.
A trip to Kirkland Air Force Base's EMP simulator in New Mexico would have shown you we were working on protection measures, and training films from my early Air Force days showed EMP shielding on B-52s on their one-way mission to the USSR during our MAD mutually assured destruction days. Today, short of keeping nukes from exploding anywhere near CONUS, we should acknowledge that there are no good national-scale solutions to EMP out there. All proposed are way too expensive, way too impractical, and virtually impossible to implement without shutting down our government, economy and military for 10-20 years. Or longer.
With a well positioned high altitude nuclear explosion (200 miles up over the US midwest), the Smart Grid, if anything, seems to make us even more vulnerable by adding more devices with easily fry-able circuitry to the mix. But in scenarios where a nuke goes off on the ground or at low altitude, distant micro grids and remote sections of a national Smart Grid would miss out on the carnage, and by islanding, would not be taken down by a cascading failure of the national grid as regional systems likely would today. So the take away is keep on building the Smart Grid, and try not to let EMP, or civilization-ending asteroids, get in the way.
Alarming Doomsday Illustration: Wikimedia Commons