Windows 8 will allow you to build applications that can be used across multiple platforms and applications that will be powered by the cloud.
There are still questions about how windows 8 will integrate with the cloud. How applications will utilize Azure, how to store data in the cloud and how to build applications that will easily interact with the cloud.
This Microsoft video from the BUILD conference is led by Microsoft employee Wade Wegner.
It covers issues like authentication, storage and notifications across a wide range of devices.