Over the past few years, Parent Technology has been using Magento Commerce to develope its ecommerce shopping carts. Multiple clients of Parent Technology have ask to use a single backend platform for gathering and managing their information; orders/products/pages/ect.
Here are two examples of multi-store fronts using magento
http://lawn-gardenproducts.com/ and
http://www.kbhardware.com
http://store.csionline.org and
http://store.csionline.org/homeschool