Features meant to increase user efficiency by reducing steps can end up hurting users if they do not conform to existing mental models and expectations based on past experiences.
Select a single radio button by default in most cases. Reasons to deviate or not: expedite tasks, the power of suggestion, user expectations, safety nets.
Should the OK button come before or after the Cancel button? Following platform conventions is more important than optimizing an individual dialog box.
Once an online form goes beyond two screenfulls, it's often a sign that the underlying functionality is better supported by an application, which offers a more interactive user experience.
User interface guidelines for when to use a checkbox control and when to use a radio button control. Twelve usability issues for checkboxes and radio buttons.