I have just installed a new drupal/ubercart website 22/11/2009. I had the same issue with images not displaying and found myself scouring the forums for a solution. Some of the solutions I found only partly worked so I decided to fiddle around myself with some settings. This solution works for me so it might do for you too ?.

Fresh install with everything up to date (all the latest versions).

Before I add new products I go to: "Administer/File System" and change the setting to "Private - files are transferred by Drupal".

When I am finished adding new products I go back to: "Administer/File System" and change the setting to "Public - files are available using HTTP directly."

I don't know why this works or understand what the issue is which prevents images from showing but perhaps this solution will help you if you are having this problem. It may also help someone cleverer than myself understand the issue and fix it.