"Collaborative filtering", "using past activity and stated preferences to guide us" I can't think of areas Amazon does worse in today than these two areas. Reviews are so untrustworthy they are just noise. Those coffee beans I ordered a month ago? I have to go back to my orders page, search (and for some reason their search is dirt slow) - then wade through unrelated products to finally find them. But oh, hey, you ju…
I have worked on the same recommendation systems. It's also the most often oncall issue. The problem is mostly due to lag in event processing (especially orders).