Check out what Google Mobile site has to say:
Finally, this updated version of the Gmail app has limited support for Priority Inbox. If you’ve enabled Priority Inbox via the desktop version of Gmail, you’ll see an “Important” label that shows all messages flagged as important. You can even add a shortcut to “Important” to your home screen.
The Gmail update requires Froyo (Android version 2.2), so it’s available if you have a Nexus One, HTC EVO, Motorola Droid 2 or Motorola Droid. (Not sure if your device is running Android version 2.2? Check here.)