Google Play Services 4.0

Today we're launching a new release of Google Play services. Version 4.0 includes the Google Mobile Ads SDK, and offers improvements to geofencing, Google+, and Google Wallet Instant Buy APIs.
With over 97% of devices now running Android 2.3 (Gingerbread) or newer platform versions, we’re dropping support for Froyo from this release of the Google Play services SDK in order to make it possible to offer more powerful APIs in the future. That means you will not be able to utilize these new APIs on devices running Android 2.2 (Froyo).
We’re still in the process of rolling out to Android devices across the world, but you can already download the latest Google Play services SDK and start developing against the new APIs using the new Android 4.4 (KitKat) emulator.

Google Mobile Ads

If you’re using AdMob to monetize your apps, the new Google Mobile Ads SDK in Google Play services helps provide seamless improvements to your users. For example, bug fixes get pushed automatically to users without you having to do anything. Check out the post on the Google Ads Developer Blog for more details.

Maps and Location Based Services

The Maps and Geofencing APIs that launched in Google Play services 3.1 have been updated to improve overall battery efficiency and responsiveness.
You can save power by requesting larger latency values for notifications alerting your app to users entering or exiting geofences, or request that entry alerts are sent only after a user stays within a geofence for a specified period of time. Setting generous dwell times helps to eliminate unwanted notifications when a user passes near a geofence or their location is seen to move across a boundary.
The Maps API enhances map customization features, letting you specify marker opacity, fade-in effects, and visibility of 3D buildings. It’s also now possible to change ground overlay images.

Google+ and Google Wallet Instant Buy

Apps that are enabled with Google+ Sign-In will be updated with a simplified sign-in consent dialog. Google Wallet Instant Buy APIs are now available to everyone to try out within a sandbox, with a simplified API that streamlines the buy-flow and reduces integration time.
Google Wallet Instant Buy also includes new Wallet Objects, which means you can award loyalty points to a user's saved rewards program ID for each applicable Google Wallet Instant Buy purchase.

New user control over advertising identifier

To give users better controls and to provide you with a simple, standard system to continue to monetize your apps, this update contains a new, anonymous identifier for advertising purposes (to be used in place of Android ID). Google Settings now includes user controls that enable users to reset this identifier, or opt out of interest-based ads for Google Play apps.

More About Google Play Services

To learn more about Google Play services and the APIs available to you through it, visit the Google Services area of the Android Developers site.