In this talk we describe two models of collective inference. The first,
based on joint work with Alexandre Proutière and Mesrob Ohanessian, deals
with categorization of a news item based on the reaction of readers
exposed sequentially. We propose policies for choosing who to expose based
on previous reactions, which achieve a desirable trade-off between
spamming, ie exposure of uninterested readers, and missed opportunity,
ie non-exposure of interested readers.