From a theoretical perspective, what you're assuming above is that you apply a social filter and then use collaborative filtering (i.e. Amazon, Netflix and simi

From a theoretical perspective, what you're assuming above is that you apply a social filter and then use collaborative filtering (i.e. Amazon, Netflix and similar's method). In fact the two supplement each other -- collaborative filtering using the entire customer database and then do a weighted merge of that with an algorithm ranking things based on social graph traversal.