Something that has still lingered on in the designing of apps, is the notion of forcing users to register/sign-in prematurely. That is, downloading a new app, you get the rude interruptive screen that asks you to enter identifiable information, before you even know if the app is worth the real-estate on your device.
Such design workflows constitute in my opinion an anti-pattern, asking something of the user before you have convinced him or her of the merits of your app. Sure, you can put promises in the form of on-boarding, but the user still hasn't gotten to use play with your app first.
UX best-practices these days dictate a preference for deferred authentication, not requiring authentication till you absolutely need it. Unless you are required to be identified, give the user as much of the app as you can, before you require him or her to authenticate, so that they can maintain a sense of persistence when they want to revisit the app, or use the app on another device. This gives the user the confidence of not compromising their information at the start, getting a sense and feel for what the app has to offer, and then volunteering his or her information.
Facebook and Twitter provide a different take on deferred authentication, which is interesting. Facebook Anonymous Login permits users to login anonymously without divulging their Facebook identification information, but gain the ability to persist not just within the app but hand-off the persistent state to another device, whilst maintaining anonymity.
The app can then offer to upgrade the user from the anonymous state, to authenticated state, at a later stage, whilst the app benefits from tracking new and unique users, they won't overstep the boundaries and identify the individual users.
Twitter have what is called Digits, their take on anonymous is also yet different. They enable login/signup using a phone number as a form of identification, something that is globally-unique.
With Digits, you don't even need a Twitter account you just provide one identifiable item, your number and you can upgrade with a Twitter Account at deferred stage. This is slightly more obtrusive than Facebook's one, but still preferred to the old model of asking everything straight up.
I for one thing would love to see a mentality change at a more consistent pace with apps, as building trust is more important than obtaining vanity information from users just to prove you have a large user base.