One of the features I really like is the estimated time printed at the bottom of the screen. You can toggle between time left in the current chapter and time left in the book. When you first use the Kindle, it doesn't immediately show you those values. Rather, it watches how fast you read and adjusts the estimates accordingly.
Unfortunately, it's easily confused. I'm reading a book with lots of footnotes, and I occasionally flip around. Rapidly changing pages appears to confuse the time estimate calculations. After a while, it was estimating I'd finish the book in one hour, even though I was at the 8% mark of a 1000+ page book.
Luckily, I found an easy way to reset the estimate. Search for
;ReadingTimeReset (keep the semicolon and capitalization as shown) and the estimate will be reset.
A couple of other miscellaneous thoughts on the Paperwhite:
I was initially disappointed by the uneven backlight at the bottom of the screen. After a couple hours of use, I found that I had the light turned on too high. Lowering the light intensity makes the unevenness less apparent while keeping the screen legible.
Once I decided to keep the Paperwhite, paying the extra $20 to get rid of the ads (or "Unsubscribe from Special Offers" in marketing-speak) was a no-brainer.