The articles are written by Luke Wroblewski http://www.linkedin.com/in/lukew
It gives great insights into the importance of desiging sign up forms for mobile apps and how to avoid potential users to drop out just after downloading the app, and actually never use it. One reason for the drop out can be: badly designed sign up forms.
Mobile Sign up Forms MUST DIE
http://www.lukew.com/ff/entry.asp?1678
Gradual Engagement for Sign Up Forms