Android 4.1.2 hit the Nexus 7 last week, and now it seems the latest version of Jelly Bean is slowly starting to make its way to the GSM/HSPA Galaxy Nexus and Nexus S. Currently the only version confirmed to have received the update is the "yakju" variant of the phone -- that's the one sold outside of the U.S. without Google Wallet support. We'll likely see the "takju" Galaxy Nexus -- the one sold through the Google Play Store -- hit 4.1.2 in the coming days. (Sorry, Verizon people, you're likely in for a much longer wait.) On the Nexus S, users in the U.S. and Canada (GT-i9020T/i9023) are reporting that they've received the update.
On phones, Android 4.1.2 is a minor update over the previous version 4.1.1. The changelog points to small performance and stability fixes. Unlike the Nexus 7, Android 4.1.2 on Nexus phones doesn't enable landscape mode in the launcher.
If you're feeling adventurous, and have the right kind of Galaxy Nexus, you'll find direct links to the OTA to flash your device manually. We'd recommend just waiting for the update to hit, though, as you're not missing out on much by being back on 4.1.1.