Available today, the Windows Phone SDK Update for Windows Phone 7.8 is an optional update that adds two new Windows Phone 7.8 emulator images to your existing SDK installation. These two emulator images should enable you to fully test how your Windows Phone 7.5 app’s Live Tiles will look and behave when they are run on a device running Windows Phone 7.8.

The SDK update requires an existing installation of the Windows Phone SDK:

• Windows Phone SDK 7.1 (7.1 or 7.1.1)
• Windows Phone SDK 8.0

If you have both the Windows Phone SDK 8.0 and Windows Phone SDK 7.1 installed on the same computer, both SDKs will be updated.

If you have a Windows Phone 7.5 app in the Marketplace, it is highly recommend downloading the Windows Phone SDK Update for Windows Phone 7.8 today and starting to experiment by using the new tile options in your app.

Via: http://blogs.msdn.com/b/bclteam/archive/2012/10/19/using-async-await-without-net-framework-4-5.aspx 

Do you want to use await but don’t want to wait until you can target .NET Framework 4.5? The waiting is over and awaiting is about to begin.

Today, we are proud to announce an update to the Async Targeting Pack we had previously released. The previous targeting pack allowed you to use await when targeting .NET Framework 4.0 and Silverlight 5. Our updated targeting pack allows you to use await in Visual Studio 2012 when targeting any of the following platforms (or higher versions):

• .NET Framework 4.0 (with KB2468871)
• Silverlight 4
• Windows Phone 7.5
• and portable class libraries targeting those platforms

So effectively we added support for Windows Phone 7.5, Silverlight 4, and portable class libraries.