We are designing and testing an automatic system to calculate the usefulness of items on Web pages. Using this system, Web sites can adjust the order of presentation, for example of reviews on a book-selling site, so that the most interesting and useful reviews filter to the top. The system works by observing the dwell-times and locations of the cursor while users browse the site, and so requires no deliberate action on the part of its users or administrators. The system can be used passively to gather information, or to feed the interest levels of past users forward in order to improve the experience of future visitors.