You can charge your iPhone with the iPad charger no problems. However, it does NOT charge any faster as the iPhone will only ever draw 1amp.
I tested this to confirm it. Ran both my iPhone 4 and my wife's down so they powered off. Connected one to the iPad charger and one to the iPhone charger. Turned on the power and both started charging. Every 30 mins I checked to see if one was charging faster than the other, both charged at the same rate and reached full charge at the same time.
Anyone seeing the iPad charge it faster is imagining it. The regular charger charges pretty fast as it does a fast charge to 80% and the slows down.