The original Kindle Paperwhite (the one released in 2012) did not get an update today. But if you have the second-gen Paperwhite or the model Amazon released a few months back then I have some good news for you.
The update adds better Goodreads integration with author profile pages and personalized recommendations, and Amazon also improved the Lookup feature to make it "easier to get to the actions you want to take while reading - highlight, create a note, share a quote, and more, while keeping your favorite Smart Lookup features like Dictionary, Wikipedia, and X-Ray easily accessible".
There's also the new typography and layout improvements with the hyphenation, justification, ligatures, and kerning that Amazon promised back in May but is still working to deliver. There's also a mention of pop-up footnotes, endnotes, and chapter notes.
Or at least that is what the change notes say; my Paperwhite has just finished the process of updating, so I can't say what has been added.
Yu can find the updates here:
image by GillyBerlin