If you are using e-commerce contributed module you may want to checkout the latest ecommerce module – “UberCart”. I have reviewed it and I have only positive things to report at the moment.
For Ubercart you need Drupal 5. Ubercart has a good look and its very easy to setup and manage while not sacrificing the key ecommerce functionality.
BTW there was a functionality I needed for my ecommece shop to Calculate Shipping by weight of Product. A simple one line code change was suggested . Here is the details.