I'm not a huge macro guy. This statement can be confirmed by either my classmates or my grades in macroeconomic courses, (undergrad A/B-, grad school C+/B). But I think my general ignorance to this aspect of the "dismal science" can actually help in providing a decent blog as to why the 2011 Nobel Prize winners in Economics, Thomas Sargent and Christopher Sims were so deserving of the honor. Reading the press reports confirms that reporters haven't the foggiest clue as to why Sargent and Sims' contributions were gigantic...
UChicago news here. (we are always quick to claim a Nobel as our own but this is really a Minnesota coup)
Excellent but probably inaccessible write up on Marginal Revolution by Tyler Cowen: Sims here and Sargent here. Alex Tabarrok's words here.
Probably the best layman read is on the nobel.org webite here. They provide a good 5 page explanation with pretty pictures. But even that would be difficult without having recently taken a macroeconomic and econometric course. Why is macro so opaque?