Not sure how it'll be pushed out, I just spotted it on another forum. Minor bug fixes and hopefully a slightly improved battery life from what I read.
http://www.androidpolice.com/2013/02/02/google-pushes-new-android-4-2-1-code-to-aosp-jop40g-4-2-1_r1-2-here-is-the-developer-changelog/
http://www.androidpolice.com/2013/02/02/google-pushes-new-android-4-2-1-code-to-aosp-jop40g-4-2-1_r1-2-here-is-the-developer-changelog/