Most designers don't test with customers. Most designers work like image advertisers talking about brand image and are far more into creativity than user research.

However, human-factors and user experience designers do extensive user testing and much more focussed on bottom-line results. That's the conclusion of How Direct Marketing and User Experience Are the Same and to a lesser degree Do It Wrong Quickly: How the Web Changes the Old Marketing Rules.

As I have written before, graphic designers are hazardous to your wealth. Not one in twenty graphic or web designers approach a project with anything like a copywriter's mindset.

Those few designers versed in the methodology of interaction design are different. Their user tests and philosophy of user response informed experimentation has much in common with direct response. And it points to what I've been saying that web design is so untested and misdirected it represents an opportunity.

As much as half of the response increasing breakthroughs which now come from copy will come from test of design changes in future.