>>A much better approach is to install significant instrumentation and actually talk to users about what's wrong with your sign up form. In my experience this

>>A much better approach is to install significant instrumentation and actually talk to users about what's wrong with your sign up form. In my experience this only works for obvious, glaring flaws, such as "I hate that the phone number field enforces a specific format" or "Why the hell are your password requirements so stringent?" But a lot of UX is about what happens on the unconscious level. A user will never tell you, "Your bright red background feels too aggressive/hostile" because they simply don't recognize it at the conscious level to be able to verbalize it. The signup or checkout form might make them feel uneasy, but they won't know why. I find that the best way to optimize websites is to do A/B testing first, and then talk to your users about the subset of the results (which might be the majority) that you find confusing or surprising. Basically, never rely on just one method, because then you will be hamstrung by the shortcomings of that method.