It will be interesting to see how difficult or how easy it is to fool Apple's fingerprint scanner. I suspect the security will not be high given the constraints of putting it in a button on a mobile phone and the preference for letting marginal scans authenticate the user so as not to frustrate or inconvenience them.

Personally, I'd trust a 4-digit pin with a lockout timer to stand up better than fingerprint authentication. It looks cool in the movies, but it's never been a very bright idea.

Of course, most won't care if it's insecure, and being able to set different functions to automatically execute based on scanning different fingers (an ability laptop scanners have had for years) is certainly a selling point.