21. A computer-based method for providing purchase recommendations on a web site to one or more customers, comprising: executing code in a computer system to cause the computer system to perform: collecting recommendation context information for a customer; using the recommendation context to identify a set of candidate recommendations; using a probabilistic model of a customer purchase decision to score the set of candidate recommendations by calculating a boost in a purchase-related criteria for each candidate recommendation using a plurality of gating factors in the customer purchase decision; and selecting the candidate recommendation having the highest score for issuance to the customer.
26. The method of claim 21 , further comprising selecting a first pitch for each candidate recommendation from a plurality of pitches based on a probabilistic model of use cases and an estimated value of each pitch for each use case.