Feature related:

Popup notification that device is plug-in is great!  Propose including supporting information for how to enable Line In to play via the home menu for first time users.  Could be treated as 2 separate popups or combined into one with icon + text as a context menu.

Is there an existing spec for the default behavior for all external devices across the product line?  We now have USB, SD card, HP, and Remote Devices (iPod, etc.)

Couple of comments:

1. Music is cut-off when transitions into Now Playing.  Is this the expected behavior? Can Line-In only be played through the home menu? If the user has Now Playing screensaver selected "when playing" it should over write the transition or work inside Now Playing.  

2. No icon appears in the status bar when music is playing through "Line-In"  We need to either display the play symbol or use a generic mini "remote device" icon where play usually appears.

3. While enabled, Now Playing screen displays what was last played by user before Line-In mode was turned on.  If album artwork and meta data cannot be displayed inside Now Playing screen need to default to text that says "Line In" and use default icon for album artwork.  If possible a visualizer would be ideal given constraints.  An alternative would be to have a screen overlay that rendered similar to an alert screen with icon + text Line In enabled.  "To turn off press back button..."