1. A computer-implemented method for determining topical interest, comprising: receiving signal information for a user of a document, the information including at least one signal value representing the user's activity with or relationship to the document and a signal weight for each signal value; computing a normalized signal value for each of the at least one signal values; computing a document interest value based on a sum of products of each normalized signal value and the signal weight associated with each signal value for the user; receiving topic information for the document, the information including at least one topic and a weight for each topic, where the topic relates to content of the document, and the weight represents a level of confidence that the topic is associated with the document; and generating an update to an interest signature value of a first topic for the user by adding a product of the computed document interest value for the user for the document and a weight of the first topic in the document.