I would like to see the option of being able to add tags to the end of the URLs on the products uploaded to Google Product Search. This would help us single out this type of traffic for reporting purposes.
Here is the URL builder tool for Google: http://support.google.com/googleanalytics/bin/answer.py?hl=en&answer=55578.
Even something like adding a custom field in the Google Product Search/Merchant Center Configuration screen that would be added to each link when the file is generated.