1. A method of estimating a probability of re-sharing information, comprising: extracting keywords from a set of documents addressed to a user; weighting the keywords from the set of documents according a metric for the user's interest in the keywords' respective source documents to create an interest model; receiving a new document having one or more keywords; and determining a likelihood that the user will re-share the new document using a processor, said likelihood being based on the interest model and the one or more keywords present in the new document.