Most of the new functions are specific to the Kindle Fire range.
The 'X-Ray' feature from Kindle Touch has been extended to Kindle Fire and Kindle Paperwhite, making it possible to see all the passages that relate to particular concepts (characters, places, etc) and to obtain descriptions from Wikipedia and Amazon's Shelfari.
X-Ray now also covers movies (using information from IMDb; exclusive to Kindle Fire HD) and textbooks (providing easy access to the book's glossary and incorporating information from Wikipedia and YouTube).
'Immersion reading' allows users to read along while listening to an audiobook, with the text being highlighted as it is spoken.
Many Kindle users will be familiar with Whispersync, which automatically synchronises book purchases and bookmarks across devices.
This concept has been extended to support synchronisation of text and audio books, so users can, for example, listen to a book while driving to work, starting exactly where they left it when reading in bed the night before (also available on Kindle Paperwhite and the Kindle mobile apps).
The Silk web browser has been reworked for faster page loads, and the email client in the new Kindle Fire models claims "world-class Microsoft Exchange integration" including the ability to synchronise the newest messages first, plus support for other popular mail providers including Gmail and Hotmail.
A new take on parental controls comes in the form of 'FreeTime' which allows parents to select the content their children can see, and to set time limits on different types of content (eg, an hour of games, but unlimited reading).