Many of the freebies I download seem to have clean chapter breaks that make good use of the time to read feature.
I put a series of four epubs I bought from Harlequin together with the Calibre ePubMerge plugin, converted to MOBI, uploaded to my PW, and it told me the total time to read was just over 10 hours, which knowing the author was correct for my typical reading speed (although it does adjust I've noticed depending on what I'm reading). Chapter breaks are present in each of the books and give me an pretty accurate time left in each chapter.
I agree. So much so I find myself looking for time left when I read my Kindle Keyboard (it goes to and from work with me for the TTS feature).