Jakob Nielsens First Rule of Usability

Jakob Nielsen's First Rule of Usability still holds true today: pay attention to what users DO - and not what they say.

This holds doubly true in what users predict they will do in the future.

Say, for example, that 50% of survey respondents claim they would buy more from e-commerce sites that offer 3D product views. Does this mean you should rush to implement 3D on your site? No. It means that 3D sounds cool. The world is littered with failed businesses that banked on people's attitude toward hypothetical products and services.
First Rule of Usability? Don't Listen to Users

When in doubt, think like Dr. House. "The patient always lies about what he does." Do not take the user's "word" for it - send out your staff to ascertain how the patient/user acts,

In short, any and all changes must improve the bottom line. It must reduce the time and effort in accomplishing a task by the users, whether they are customers or employees.