The software update includes general improvements and the following feature enhancements:
Improvements when buying from a book sample
While reading a sample of a book, you can view the price of the full book and purchase from the reading toolbar with one tap.
View full definition when looking up a word
When you look up a word in the dictionary, you can now view the full definition in the definition window.
Search enhancements
You can easily search for a highlighted word or phrase in your book, your items, or in the Kindle Store. Highlight the word or phrase, tap More, and then tap Search.
http://www.amazon.com/kindlesoftwareupdates/touch