A solution to a common problem.
I have built a number of Drupal sites, but this was my first with Ubercart. It's August 27th 2010.
I simply couldn't get images to appear anywhere other then in the main Product page. Al;l modules etc seemed to be installed and on.
I checked the file structure and found that although my Imagecache Admin said that a bunch of Ubercart presets existed, guess what, no directories for them in files.
Solution - for each Preset, click "Override" and then save. This forces the creation of the right files directory and then it seems to work. (Yes, I know this the Drupal eqv of hitting the damn TV in frustration, but hey, sometimes hitting the TV works).
NOTE - I hit this right at the start of the set up so only had one test product, which I deleted and re-entred. If you have existing products not sure if it will correct for them, but if not automatic, try FLUSH before panicing and reloading all existing products.