Don't know if this the appropriate section...
I very much like that the Paizo site keeps track of what I order, because sometimes cover art changes or I get forgetful of whats in my collection.
I would like the option of informing the Paizo site of the products I already have in my collection (acquired elsewhere) and have it keep track of them too.
That way, I won't accidentally buy something I already have. It would prevent return issues, and Paizo would get marketing info out of me on what I buy from the FLGS, what I like and make suggestions on relevant related products.
It should go to Website Feedback section.
I know that Paizo shop already keeps track of electronic purchases, I don't know it keeps one for physical purchases but it could probably be (relatively) easy to add tracking physical purchases - it would need a separate set of flags for physical products bought, though. It would be nice if the user could also manual flag on his account section products he purchased in other venues to avoid accidentally purchasing things he already owns from other sources.