I love my TrackIR5. It sets the bar of immersion so high I can't play another sim without it.
Here are a couple of gameplay videos featuring TrackIR 5 in Apache: Air Assault. Actual recorded gameplay from inside the cockpit and replay video footage from outside the chopper all use TrackIR 5 for camera orientation:
[video:youtube]http://www.youtube.com/watch?v=GYJjjXl5DIc[/video]
[video:youtube]http://www.youtube.com/watch?v=roeUs-48AcA[/video]