I have been working on a retail for a very long time now but the stumbling block I keep coming up against is the ecommerce modules. I used joomla with an ecommerce module but didn't find either of them particularly organised. I moved onto Drupal and decided that I would learn Drupal 7 but I've been trying to install various ecommerce modules for Drupal 7 such as ubercart and drupalecommerce but utterly failed and I've been getting nothing but errors. I was the furthest with ubercart but I couldn't add any attributes to the product types.
Drupal 7 is in the process of being ported, and I hope to be released very soon. Since the release for Drupal 7 will be a direct port of the 6.x-4.0 the upgrade should not take too long to complete. However I do feel strongly that we will not be able to make a final release until all the dependent modules, views, views bulk operations, rules, and ctools have stable releases for Drupal 7.x The currently have development releases and some have alpha releases, so I don't expect this to be too much of a holdup.
The shared link by "RajanUrs" regarding drupal and ecommerce is very useful. Here you can easily see which ecommerce module best support to which drupal version. It will help to take decision before using that module for your website.