For those developers with App Hub accounts can now register (unlocked) a Windows Phone to their App Hub account even if it was unlocked by another account. For those not familiar, a registered Windows Phone basically allows developers to side load apps that are in the works to their Windows Phone for testing. This gives developers a lot more flexibility such as borrowing/sharing various Windows Phones for compatibility testing.
Additionally, the registration of the device expires annually and used to require re-registration from the original account. Now, all developers need to do is re-register the Windows Phone from an active App Hub account. For more information on starting an App Hub Account, you can find all the details here at the App Hub Website.
Source: App Hub Forum