Google started rolling out the Android 4.2.2 update for some of the Nexus devices a couple of days ago. Although there was no official list of improvements released for the new version, we are now seeing reports from people who managed to get the update on their device.
Android Police has made a short list of new changes that were made in this version of Jelly Bean. The major one seems to be the ability to use the notification screen shortcuts as actual toggles, something that was not possible before (it would take you to the particular option in the Settings app). Although they still behave the same way as they did before if you just tap them, long pressing on some of the shortcut buttons, such as Bluetooth or Wi-Fi will instantly enable or disable these features. Meanwhile, a single tap is now required to enable or disable Airplane mode.
The other fairly major change is the addition of a new notification sound that plays when you place the device on a wireless charger. There is also a new sound for low battery notification. You can find the sound samples in the source link below.
Lastly, new app downloads show percentage and estimated remaining time in the notifications.