Android Police notes that Google Play Books has gotten an update that allows you to upload e-books into its cloud directly from your device, rather than being restricted to doing it only via the web site. I hadn’t realized Google Books could do cloud storage of your own e-books at all, but given that Google Play Music does cloud storage of your MP3s, I suppose I should have guessed. Need to see about trying that out.
There are a few other improvements, too, like landscape mode, lower brightness settings for low-light reading, and so on. The update probably won’t hit devices for another little while, but the Android Police article has mirrors for downloading the cryptographically-signed APK of the new version of the app.