Hardcover plus Kindle Version: My wife helps organize the Authors Night book fair in East Hampton. It would be great to get a signed copy of Bob Caro's book and get the electronic version to read it.
A real progression indicator: How close are you to finishing based on the book, not the appendices. I recently read The First Tycoon, and the book essentially ends at the 73% mark. I could feel the book winding down, but kept seeing the percent read not making sense.
Reading Stats: Word per minute, statistics on your reading consumption, your consumed word asset allocation (fiction, non-fiction, history, etc). Imagine Morningstar's X-Ray feature but applied to your reading.