[vanilla swirl]

90% would be gone in one year

http://www.futurescience.com/emp.html
http://en.wikipedia.org/wiki/EMP
http://www.empcommission.org/docs/A2473-EMP_Commission-7MB.pdf
go read the book;
http://www.amazon.com/One-Second-After-William-Forstchen/dp/0765317583/ref=sr_1_1?ie=UTF8&s=books&qid=1250759390&sr=8-1

If you do a search of news articles of about a year ago there was talk of NK and Iran wanting to develop Emp technology with their nuke programs. Nobody is talking about it today. Go to the first link above and it seems that the most efficient Emp producing device is a more primitive device the likes of which NK and Iran are capable of.
I did notice a news article a few weeks ago about preparing DC against EMP but can’t find it now.
I read “One Second After” and it scared me to death.

[To-Whose-Benefit?]

It does kinda look like we passed that Tipping point, where once the Electorate realizes that it can Vote itself largesse from the public treasury, it’s All downhill.

[RayChuang88]

Only one thing: you need a megaton-yield nuclear weapon for EMP to be effective. And alas, that's beyond the technology of North Korea or Iran--a 20 kT nuclear device exploding in Earth orbit has the effect of a solar storm. After what happened to the Quebec power grid in 1989 when a major solar storm knocked out part of the grid, they've put in more sophisticated safety systems to protect the grid from the effects of a solar storm, so a low-yield nuclear weapon will have relatively little effects on the ground below.

According to what we know about the Dominic Starfish Prime test, it used a W49 nuclear warhead (essentially a modified B28 nuclear bomb) with a yield of 1.4 MT. As such, the explosion at 250 miles above the ground had pretty awesome effects, as witnessed by the substantial electrical interference in Hawaii. It makes me wonder during the Cold War, the Russians had planned to use the older SS-9 (R-36) missiles armed with a circa 20 MT nuclear warhead to detonate about 200-300 miles above the ground for enormous EMP effects.