Earlier this morning, Microsoft announced Windows Phone 8 at the Windows Phone Developer Summit. Before I start, existing Windows Phone 7.5 (Mango) users will not be able to upgrade to Windows Phone 8 due to hardware differences and hence they will be getting a minor update dub Windows Phone 7.8 in a few weeks time that bring some changes to the start screen for existing users.

My summary of Windows Phone 8 from the summit:
Hardware

Windows 8 Start Screen
Windows 8 Start Screen