The User Guide says:
In books, the progress indicator also shows you the overall percentage of the book you have read and a numeric location of where you are reading, so you can easily find a particular passage or reference it to your friends. Locations are the digital answer to page numbers. Changing the text size on Kindle also changes the page numbering, but with locations, you return to the same place every time regardless of the text size.
I still prefer page numbers with text change but I'll take the percentage number; it's way better then the progress bar alone!
