It gets shmutzy and won't read your fingerprint until you clean it. This might involve pressing it hard enough to activate Siri. This is not a bad problem to have, "boo hoo I have a smart phone my life sucks."
When it came out, there were far too many breathless articles about how someone could make a rubber copy of your fingerprint and then hack your phone. This was stupid, and everyone knew it was stupid, but people wrote about it anyways. (And apparently a lot of people don't even have passwords at all on their phones, so....) In order to do this, you'd need to steal their phone and make a rubber copy of their fingerprint. How many times has this happened? Zero. Why? Because the internets would blow up if it did, and that hasn't happened.
|(Photo credit Apple Inc.)|