If you're asking as a developer, you can find information on how both Metro style apps and Desktop apps can raise notifications in the
Toast notification overview .
IUserNotification
and
Shell_NotifyIcon notifications will show only in the desktop.
If you are asking as a user then general consumer questions should go to the Windows 8
Microsoft Answers community. IT Pros discussions should be posted on the TechNet forums under the
Windows 8 IT Pro category. This forum is for developers with questions about writing Metro style apps.
--Rob