Per this old post, I think having a BACK button that can be enabled on the product page to either take a visitor back to the previous page, or back to the product list or Category page would be a great idea.
http://www.ubercart.org/forum/support/405/back_product_list_link_or_button
I just completed a usability review of my store prior to launch, and it was the number one requested item by a small focus group.

