In addition to the usual bug fixes, tweaks, and improvements, this update adds something that I've been wanting to see for years now. The Kindle Android app finally supports a 2 column mode when you're reading in landscape mode. Note that it only works in landscape mode, not portrait mode, but it is much better than nothing.
Like any reading aesthete, I used to despair over the way the Kindle app displayed text in landscape. The lines were far too wide to be read comfortably on a 10" screen, and that limited me to only reading while holding my tablet in portrait mode. While that is a workable option it never fit with how I wanted to use the the tablet. And to be honest, even on a 7" tablet the lines of text were too wide before this update.
This update also adds some customization options (margin and line spacing).