Amazon announced via press release that it will be releasing a new version of it proprietary MOBI format. This comes on the heels of the recent finalization of the EPUB3 spec, which is the open standard eBook format used by pretty much everyone except Amazon (e.g. Barnes & Noble, iBookstore, etc.) The new format will hopefully be a vast improvement over the previous MOBI format used by Amazon, which left many a self-publisher frustrated due to its erroneous rendering of tables, lists, and images.
The Kindle Format 8 is based on HTML5 and CSS3, which is geek-speak for the current standards of web design and development. The new HTML5 tags (such as <section>, <nav>, and <article>) are more geared toward developing more pretty HTML source code and not very exciting for the average eBook reader. However, CSS3 is a way to "style" the eBook in new ways. You can do lots of fun things with it to improve the reader's experience like adding animations (for an example see my social media icons on the right sidebar), adding shadow effects (see my wife's business' website), and even adding headers and footers to every page with the @page feature.