I've had to redo my prints a couple times since September, quickly learned to do 2 for each thumb. Once in a while it doesn't let me in, but it's rare. Yesterday, however, it kep saying Try Again over and over (it didn't change to Slide to Unlock). I tried both thumbs multiple times. I know I could've just entered my passcode but I wanted to know if I would have to reset my prints. I ended up pressing the Home button and it let me in! I said to myself 'wow, great security Apple!' In retrospect I don't think just anyone could've got in- what I think happened was that it did read and accept my print, but there was a bug/glitch where it wouldn't take me to the Home screen. At least I hope!
To the poster who mentioned Siri in the car/voice metrics- I'd like to add that I wish they would implement a voice activation for Siri (apparently you can only do it with a jailbreak). My hands free experience while driving isn't currently 100% hands free. I know what people are thinking- 'well then your battery life would drain because Siri would always be listening, which is also creepy' but if there was a toggle in Control Center for voice activated Siri for when you get in your car, that would be awesome and give me a truly hands free, non-distracted driving experience.