Google has officially announced the rollout of Android 4.1 for Nexus S handsets on T-Mobile, H3G, O2, Rogers, and Vodafone in "most countries." The company began quietly pushing the update out to some Nexus S owners earlier today, and Google's Plus page stands as official confirmation. You'll need to be running the stock IMM76MD ROM in order to update to JRO03E, which includes the speedy Project Butter improvements, Google Now, and other Android 4.1 goodies.