My participation in this site is limited to a couple of specific areas (see below). I did not design the site nor do I maintain the graphics or content. The site is a highly-customized Drupal 6 site with UberCart, plus a number of custom modules. The coolest thing about this site is it uses "crowd-sourced" artwork as the basis for all of their products.
Custom Tag Creator
My first task for DogTagArt was to simplify and improve the upload process, by creating a new Custom Tag Creator function. This tool allows a customer to upload their own artwork or photos to the site, then zoom, position and crop the image to fit the tag shape. It includes a real-time viewer so the user can immediately see what the end result will look like.
Prior to writing the Custom Tag Creator, potential artwork contributors had to create and submit 2 carefully-sized and shaped images based on a specific .PSD template. This had limited the target audience significantly, so this new tool greatly expanded the business.
High Performance Drupal site
My second task was to address performance issues as the site grew by moving the site from a normal Drupal install on Dreamhost VPS to a Pantheon Mercury 1.0 image running on Amazon's EC2 "cloud". This image features the Pressflow Drupal 6 distribution with a Varnish 3.0 front end serving as a reverse proxy. This combination provides for spectacular speed (for anonymous users), plus the awesome flexibility and configurability of Drupal's database-driven content.
However, to get the full benefit of Varnish, the site MUST be built carefully, especially regarding sessions and cookies in general. The original DogTagArt.com did not adhere to these practices, so I had to work to remove these after-the-fact. I go into details of this process here.
I also installed Munin and configured key charts so we could analyze the actual performance history of the DogTagArt.com site. This is an invaluable tool to insure you are working on the proper performance issues, and to evaluate the effectiveness of each change.