A user asks: "It would be nice if it was possible to deactivate the notifications for DVD playback. (but make them still appear if you play games) "
What I do when I'm watching DVDs is to set my online status to Busy. That disables all the online notifications. When I'm back into the Dash or a game, I set my online status back to Online.
You can also set your online status before you sign-in: Press the Xbox button to start the Guide, select Personal Settings and the Online Status you want.