Interaction Elasticity

Usage goes down as interaction costs increase. User motivation determines how fast demand drops, following an elasticity curve.

Nielsen, Jakob. Alertbox (2008). Articles>Usability>User Interface>Interaction Design

Usability Tips for Your Application (Part I)

There are a exponentially growing amount of applications being developed. Some of them vanish at an early stage, while others grow to be quite (and sometimes extremely) popular. What really dazzles me is how sucky many of them (both the popular and the unpopular ones) are regarding how they deal with user-interaction.

Odden, Michael. Unlimited Edition (2009). Articles>Usability>User Interface>Interaction Design