“This was one of the biggest design challenges that we faced in the update: how to be faithful to the structure and behavior of Tweets that users expect elsewhere on Twitter in extremely low-resolution views? How to accommodate touch, pointer, and five-way input methods gracefully? We took a hard look at the numbers and tested at least three different versions before we made a decision.”

Link: Overhauling mobile.twitter.com from the ground up (twitter.com)