If you slightly smear your finger every time you remove it from the sensor you shouldn't have this problem. Additionally, if you are keeping your phone in your pocket, as I do, pull it out and take a look (like I just did) and you'll be hard pressed to see much of anything resembling a useful print. I use my phone pretty much all day long and it is devoid of useful prints.

Does that mean you couldn't find my prints in other places? Sure. But I can probably find your keys in other places, too.

We know that SSL is generally not implemented properly, that the CAs are probably all hacked or subverted by the NSA, that the NSA may have developed backdoors to a number of the more popular encryption suites, but I don't hear anyone running around demanding Google or Facebook disable SSL.

If you are doing something that requires sufficient security that you don't want someone to access it via your fingerprint alone, add additional layers of security.

If you are doing something potentially incriminating ... don't do it on your freaking phone because it's probably been exploited in a dozen other ways by various authorities who can use it to find out most of what they need without being in physical possession of the phone anyway.

Most people aren't worried about the mafia or the CIA or the NSA. Most people don't even bother using a passcode, let alone a passphrase on their phones. If you can add something as easy to use as this, then it adds an additional layer of security against the casual abuse most people will find themselves subjected to (random people making calls from your phone, spouses spying on their email, etc.).

If you are worried about the CIA and the NSA, using a phone at all for anything is probably not in your best interest at this point.