Android Jelly Bean, which is currently on version 4.2.1 in the AOSP has just been made available for the OG Transformer (TF101). The custom ROM update 4.2.1 cooked by XDA Forum Member RaymanFX brings with it several small fixes that are relatively minor in nature. This custom ROM (also available under the name of CM10.1) includes the new features, such as the new keyboard, extended quick toggles, 4.2 camera with Photosphere and many more.
As of now, Camera, Bluetooth, Front-facing camera and Mic are not working. I tested the ROM and can confirm that the back camera is working properly (movie, panoramic and normal photo). I have faced an issue with Google now where the app starts and it tries to load some card but crashes. The build is plagued with few minor bugs and the dev is working hard to iron them to release a relatively bugless build in no time.
The factory images of Android 4.2.1, which should be of a bit more use to most, will be available in the coming days. Head over to the xda-devs forum to snag the build today.