Within 24 hours of releasing the Android 4.1.2 factory images for Nexus 7 and Galaxy Nexus takju variant, Google has uploaded the factory images for Nexus S worldwide version as well as yakju version of Galaxy Nexus.
These images can be downloaded from Google Developers website now.
You can use these images to update your devices to Android 4.1.2 using guides or toolkits available at XDA forums. There is still no word on OTA update roll-out, which should be start soon.
Recently released Android 4.1.2 brings landscape mode in stock launcher for 7-inch and less display size devices, performance improvements, one finger expanding/collapsing notifications, stability enhancements and bug-fixes.