1. A method for determining the similarity of computer software application interfaces, comprising: performing a comparison of structure within a first region of a baseline interface of a computer software application with structure in a corresponding region of a comparison interface of the computer software application, where a region-level measure of the first region meets or exceeds a predefined minimum level of user interaction, thereby determining a first similarity measure between the baseline interface and the comparison interface; performing a comparison of structure within a second region of the baseline interface with structure in a corresponding region of the comparison interface, where a region-level measure of the second region does not meet or exceed the predefined minimum level of user interaction, thereby determining a second similarity measure between the baseline interface and the comparison interface; applying a weight to the first similarity measure that is greater than any weight applied to the second similarity measure; and determining a combined similarity measure from the first similarity measure and the second similarity measure.