Discovered a curious bug and not sure if this is UC or Drupal related. If comments are enable for the product content type and an user submits a comment and then clicks the "Preview" button on the comment form they are then taken to the preview page. Now if they click "submit", instead of the comment being submitted the product is added to the users cart.
I'm not sure if this was the case in D6?/UC2 but I did use comments on one site and didn't see this.
You can test it out here http://dev.ubercartdemo.com/node/1
I tested this with Garland and Bartik. At first I thought it was my theme that was the issue but not so.