As great as the above sounds, there is one potential problem included with all the cool features. After you install this update you'll be able to lock down certain aspects of your Kindle, access to the web browser, Kindle Store, and your online archive of bought and uploaded ebooks. That's exactly what the Kindle Fire Got a few weeks back, and Amazon still hasn't fixed the problems it caused.
You can find the update on the Kindle support pages or you can wait for it to be sent out over the next few weeks. I'd look into setting the password before you install this update. Or you could plan on disabling the new security feature as soon as it's installed. (Better safe than sorry.)
My K4 is not in the same state as I am at the moment, so I cannot test the new features. But I'm looking forward to reading reports about the new stuff.