- Only apps which are specifically written with HDMI out work. In particular: Video and YouTube
- Photos, Safari and Angry Birds don't work.
- Music app plays through the HDMI cable, so you don't need another audio cable.
iPad (and I think iPhone 4S)
- Apps written specifically with HDMI will do whatever they're programmed to do. E.g. YouTube will display controls on the iPad and video on the TV.
- Apps written without HDMI e.g. Notes, Safari, will mirror their display on the TV