Mr. Grant, Sir. The application was developed by a company called BBflight.
http://www.bbflight.com/ It will run on the iPhone, and may run on the iPad. Their documentation says that it needs a gyroscope, which is present in the iPhone 4, and the iPad 2. I have an iPad 1, so I have not tried it.
It does have an available database, of North America. The app is $4.99, the NA database is $2.99. One shortcoming I see with it is that it only gives you the option of selecting "nearby" airports. However, in an emergency, that's what you most want to see.
It is remarkably sensitive. You would want some sort of windshield mount, to reduce the vibration, and hold it in a stable attitude in the aircraft. Holding it in your hand makes it difficult to accurately determine your attitude.
I have flown in Herb's Skymaster with it, and in my neighbor's Aeronca, and it works very well.
I will add that I had the application called iHUD, and it does not work.