I created an ecommerce portal called AssortedProducts.com which uses WordPress.
We started with the Twenty Twelve theme, but changed it in several places for the CSS like making it wider and adding CSS 3 to it. It uses several WP_Query loops and works with Grabzit to create the screenshots of each online store.
The slider uses the Promotions plugin which creates a custom post type.
The featured categories uses a custom menu loop.