An excerpt from http://www.sitepoint.com/7-mobile-ux-mistakes/, by Lynn Wang
Making changes on mobile UX can be a tricky process, especially if you come from a web background. In mobile, developers have more constraints, including screen real estate, attention times, and UI control limitations. Improving the mobile experience is always a learning process full of trial and error, so this list will get you on the right track by helping you steer clear of common pitfalls.
##Mistake #1. Assuming your users need to sign in
Everyone knows there are a ton of benefits to having users sign in, yet it’s also a significant pain point for your users. Who doesn’t get impatient having to type in the same personal data hundreds and hundreds of time for each app or service?
Most apps’ solutions are to allow users to temporarily skip registration so that they can try out the app and get a sense of value.
While this method works well enough for Apple to adopt it into their User Experience Guidelines, cutting the funnel even further can have huge benefits. If registration is a pain point, why not see what happens when you remove that pain entirely?