It crossed my mind that things like AVG's "Do Not Track" which blocks ad networks, and Firefox's Ad Block Plus feature which blocks actual ads, will Google Shopping listings appear since they are technically product listing ads through Adwords? I know the default for Ad Block Plus allows ads on Google, but a simple toggle in config will change that (as I did).
This is also a long term question. As these type of add-ons, plug-ins, extensions, and software become more popular, aside from putting an end to things like Adwords reducing income for websites, will Google Shopping become useless?
Just a thought.