I know this program has been discussed some in the "Anything Else Amazon" section (http://www.kboards.com/index.php/topic,242355.0.html
). . . . but this is about the books.
Initially, there were just over 1000 titles, some of which were magazines. All were also in KU. That number hasn't changed a lot since the program started in October. I check every few weeks or so when I think about it.
So, today, I was wasting time and browsing around Amazon and clicked the Prime Reading link. As of today, there are just over 1500 titles available. Also, when you go to the main page, there are sections for different genres, etc.
The top one now says "new and notable" and definitely includes titles that were NOT there the last time I checked.
The next section is labeled "borrow before they go" -- which makes me think their time in the program is limited.
I'd definitely recommend Prime members check out both those lists, especially the second one as it appears that if you borrow it now, you can still keep it as long as you like, even after it's no longer in the program.
I appreciate the Zon highlighting ones that might be going out in time for procrastinators to borrow them.