A content maintenance system uses a time-dependent precipitation function for iteratively augmenting or removing content over time, after an initial demonstration of user interest. A plurality of parallel precipitation processes can be launched simultaneously in response to different facets of a user expression of interest. Precipitation is dependent on highlighting or extracting segment descriptors from content of interest to the user. Then segments are filtered, rated, annotated and/or prioritized from that content. The remaining segments are matched against stored search structures. When the segments match, they are precipitated out for storage and can generate new search structures.