The Windows Phone Developer Tools update includes a MUCH improved Bing Maps control from a performance standpoint and two additional tools to assist with development. 

The first tool helps application better understand certification requirements for their application.  If your application requires a particular capability, be sure to review the related certification requirements in the AppHub documentation here: Windows Phone 7 Application Certification Requirements [PDF].

The second tool is absolutely critical if your application works with media, whether photos or videos.  It permits media access and video playback while connected to Zune and debugging.  If you try to play a video when connected to Zune and debugging, you get a default AG_NEWORK_ERROR message but in reality it is the fact that the application is connected via Zune and synching media.  The WPConnect tool located at %ProgramFiles (x86)%\Microsoft SDKs\Windows Phone\v7.0\Tools\WPConnect.

Additional details….

Windows Phone Capability Detection Tool – Detects the phone capabilities used by your application. When you submit your application to Windows Phone Marketplace , Microsoft performs a code analysis to detect the phone capabilities required by your application and then replaces the list of capabilities in the application manifest with the result of this detection process. This tool performs the same detection process and allows you to test your application using the same list of phone capabilities generated during the certification process. For more information, see How to: Use the Capability Detection Tool.

Windows Phone Connect Tool – Allows you to connect your phone to a PC when Zune® software is not running and debug applications that use media APIs. For more information, see How to: Use the Connect Tool.