Learning GCM ( for ADD7 )

One thing we all agree is a focuse on learning  "Google Cloud Messiging" aka GCM. To prepaire for ADD7 here are Google's own background documents, API and sample code for GCM:

GCM is part of the "Google Services" thus this is the highest level:

http://developer.android.com/guide/google/index.html

Google Cloud Messaging (GCM) for Android:

http://developer.android.com/guide/google/gcm/index.html

GCM Demo Application:

http://developer.android.com/guide/google/gcm/demo.html

Making the Most of Google Cloud Messaging ( GCM ) From Advanced Android Training:

http://developer.android.com/training/cloudsync/gcm.html

Please add related information to this theead so that durring ADD7 we have everything in one place.