The WSJ notes that reliability and ease of use are key and will be essential for widespread public adoption. The iPhone 5S will, by far, be the most high-profile consumer electronics device with a fingerprint scanner. Apple purchased fingerprint sensor company AuthenTec in July 2012 for $356 million.
To add to that, top notch security needs to be incorporated into this technology. Meaning, the sensor cannot be easily defeated by trickery and well known methods that work against so many other sensor devices.
I'm confident that the security experts and bad guys alike are going to go to work on this as soon as they can. If Apple hasn't made this bulletproof, they're going to have their biggest bomb in a long time.
I hope, for Apples sake and those who will use the new sensor, that this will be robust and successful.