Every time I finish a book I get the popup to rate with stars. So far those stars haven't gone anywhere, not as reviews. But I am pretty sure they use them for recommendations. It also puts it in my "read" shelf on goodreads automatically as I have that turned on. So they already have been tracking that stuff for a while. Be nice if they implement it fully. Those books stay at 100% even while on the device. Of course I have "read" collections so they go in there and I don't see those books anymore the way I have my collections set. I only see stuff I haven't read yet.
They have been playing with some stuff. I just got the "you read 27 days in february" on my home view page. I like stats.
