This study provides many insights into the features that users look for in interface building tools, as well as those that can hinder their use. The results suggest that users are willing to pay a high price for a reliable tool that will combine both fast prototyping and fully operational target interfaces and at the same time provide high functionality. Yet users want a tool that is easy to use and to learn. This is a great challenge for developers of interface builders since there is currently a compromise to make between tools that allow fast and easy prototyping, and toolkits which provide high functionality and good execution speed.