The app now features a suggestive search function where users are offered names as well as titles from their library.
The other new feature is an addition to the series page. Play Books now tells you when there's a new addition to one of the series in your library by adding a badge to the series icon (it's the little blue dot you can't quite see in the screenshot).
This would be a useful feature if Play Books were a decent comic book app, but even so it's still going to help readers stay on top of their favorite series.
In related news, Android Police tore down the app and found that the code hints at some type of integration between videos and ebooks:
It looks like Google is going to make recommendations for books when they are mentioned in videos. There's not much to explain this feature quite yet, so I'm imagining quite a few ways for something like this to emerge. My first thought is that this will harvest recommendations made in YouTube videos and carry them over to users.
There's not enough detail in the code to show how Google will use this feature, but it's worth keeping an eye on.