1. A method of measuring changes in interest of a community of users, comprising: obtaining user fingerprints of users that constitute the community at a first time, the user fingerprints comprising vectors whose components are scalar cumulative weights associated with topic categories; combining the vectors that comprise the user fingerprints to obtain a first community user fingerprint; obtaining user fingerprints of users that constitute the community at a second time, the user fingerprints comprising vectors whose components are scalar cumulative weights associated with topic categories; combining the vectors that comprise the user fingerprints obtained at the second time to obtain a second community user fingerprint; and calculating a mathematical difference between the first community user fingerprint and the second community user fingerprint.