18. A non-transitory computer storage medium having computer executable instructions which when executed by a computer cause the computer to perform operations 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 updating an interest signature value for the user of a first topic by adding the product of the computed document interest value for the user for the document and a weight of the first topic for the document.
19. The non-transitory computer storage medium of claim 18 , which further causes the computer to perform a further operation comprising: updating an interest signature value of a second topic for the user by adding the product of the computed document interest value for the user for the document and a weight of the second topic for the document.