Seems, if a SE was trying to optimize their own product (the SE), that they would look information AVAILABLE (in the cookies or elsewhere) including "this website/URL is obviouslyan important link for search term "X" because the customer not only clicked on it, but he actually clicked the "add to cart" link and BOUGHT something! There's nothing better to help our engine's search results/ reputation than to know that" (since nothing speaks more loudly than the customer's actions).
And, since that has to be true, then why WOULDN'T search engines use the data from customer cookies to examine the cookies for "add to cart" type language? That would TELL the SE that "wow, that was a great link for the item they searched for. Let's rank it high!"
Not that we can do anything about that, but fascinated, with how competitive SEs are with one another, isn't this feasible...or does it already happen. Generally, what do you think?