[ElefantPhace][1] provided an answer for Music.

Here's for [Books][2]:

> You can access your books on different devices, including compatible
> Android devices, iPads, iPhones and iPod touches, or on the web on
> your computer. No matter where you read your books, when you're
> connected to a network (via Wi-Fi or a data connection on your device)
> we'll automatically keep track of your reading place, so you can pick
> up right where you were last reading the next time you open your
> ebooks
> 
> Note: **In rare occasions when a user tries to access books on a number of devices at the same time, our system may temporarily block
> them from opening new reading sessions.** This can happen when too
> many readers are open on different machines or browsers. If your other
> reading sessions are closed or inactive, you will be able to read in
> this browser after a short delay. If you believe this is an error
> please contact our support team.

  [1]: https://android.stackexchange.com/users/30793/elefantphace
  [2]: http://support.google.com/googleplay/bin/answer.py?hl=en&answer=179841