The Windows Phone Developer Tools January 2011 Update includes:

• Windows Phone Emulator Update – Exposes copy/paste functionality in
  the Windows Phone 7 emulator. For more information, see How to: Test Copy and Paste
  in Windows Phone Emulator. End users can use the copy and paste
  functionality only after receiving the corresponding update to the Windows Phone
  7 operating system.

• Windows Phone Developer Resources Update – Fixes a text selection bug
  in pivot and panorama controls. In applications that have pivot or panorama
  controls that contain text boxes, users can unintentionally change panes when
  trying to copy text. To prevent this problem, open your application, recompile
  it, and then resubmit it to the Windows Phone Marketplace.

• 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.
• Updated Bing Maps Silverlight Control – Includes improvements to
  gesture performance when using Bing™ Maps Silverlight®
  Control.

WPDT Fix includes:

• Windows Phone Developer Tools Fix allowing deployment of XAP files
  over 64 MB in size to physical phone devices for testing and
  debugging.