I use Bigcommerce for an auto parts website of mine called Geared World.com.
We sell auto parts dealer direct and we use the Platinum Plan with Bigcommerce. We use Bigcommerce as a CMS system for our products that integrates with catalogs that we sell from. Bigcommerce is the engine behind our business as we have one million products to manage. Their Product .CSV upload times are extremely quick as compared to other off-the shelf E-Commerce providers out their on the web such as Shopify.
The biggest business problem that Bigcommerce solves for us is unlimited product storage and fast upload times.