I have been actively developing BigCommerce for the past three years. My experience would be less as an end user or shopping cart administrator, but generally have gotten positive feedback from this cart. I find the front end templating system to allow for rapid development and it seems to support any design with minimal effort. In some of the reviews I have read, it was stated that in comparison to Shopify, BigCommerce was more difficult to develop. I find them both pretty marginal.
BigCommerce is sold as a service shopping cart software. BigCommerce is priced around $30 to $200 per month. The cost depends on the amount of data / storage being used as well as if there is a built-in transaction fee. The lower tiered cart does have a fee associated with it at 1.5%. This amount can add up pretty quickly at which point it will make sense to upgrade to the next plan that does not have a transaction fee associated with it.
BigCommerce seems to have the most functionality as any of the self-hosted carts available for download. There may be a higher learning curve, but as a developer, it is to the benefit of my clients. I find that integration with Google Analytics is much easier with BigCommerce than the other hosted carts. I do find BigCommerce to be more SEO friendly out of the box than Volution or Shopify.
Another feature I found useful for BigCommerce is the iPhone app that can be used to view and manage the store in “real time.” Being that most of my clients would be on the go, this is in itself a pretty big selling point. However, while I have not experienced this myself, of the three major hosted carts (Volution, Shopify and BigCommerce), BigCommerce seems to rate lower in custom support.
A disadvantage to BigCommerce would be its lack of native blogging solutions. The build I have done had to be built alongside a WordPress build, which means to achieve any type of blog, you basically have to build two sites, side by side. This equates to almost double the work.