The IMF has written a good paper on Okun's Law (here), suggesting (from the abstract) that: "Okun’s Law is a strong and stable relationship in most countries, one that did not change substantially during the Great Recession [and] accounts of breakdowns in the Law ... are flawed." nothing new really; I have said so a few months ago (here). Bill Mitchell has good post (here), which suggests correctly that the problem with the recoveries is not Okun's Law, but excessive fiscal austerity. I would add one more thing, not only Okun's Law works well in developed countries (advanced economies according to the IMF paper), but also in developing countries. Figure below is a crude representation of the Law for Argentina.
Note that the coefficient is more or less the same as in the US or other advanced economies. An increase in GDP growth of 1.87% reduces unemployment in 1%. Close to the 2 to 1 ratio. A more sophisticated and better estimatimated version that takes into account trend issues associated with Kaldor-Verdoorn, by Fabián Amico, Alejandro Fiorito and Guillermo Hang is available here (but in Spanish).