Perl Personalization Engines

I've been sitting here trying to checkout my purchases at amazon.com 
for the last 30 minutes now and every time I'm about to log out, some 
new Perl/Apache book catches my eye in the sidebar and I end up 
adding it to my cart too... I hope to be checked out by noon at this 
rate. :)

Amazon.com uses Perl heavily, but the exact technologies behind their 
unrivaled personalization engine are of course not disclosed.

Would anyone care to hypothesize how one might architect such a 
personalization server using open-source Perl modules?

I guess it just boils down to making weighted correlations between 
the categories that they have for products and member-created lists 
and your frequency of searching for and buying things within those 
categories.

I consider this topic to be somewhere between informatics and AI, so 
I hope this isn't considered too off-thread.

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