Some feedback I've received via Twitter includes the need for shopping carts to provide better documentation on how to implement and modify their carts... the ability to better understand what PHP files to modify, etc.
 
Their opinion is that a company that can do this well would make a nice profit and suggests that perhaps Magento or someone like them might be capable...

We do not want a cart that builds the website. We prefer to have a cart that you call with the product ID and the cart id basically a user interface to the product database.
 
What I prefer is NOT available. I would prefer to have a hosted solution that would make changes when we need them. I use RomanCart which has many features, but you can not do something that seem to be an obvious need, like override Ground shipping to offer it free, yet still offer expedited shipping to the customer. When you do offer Free shipping, you need to make the weight zero lbs so no other method can be offered to the customer.
 
As an alternative, would be nice to have a hosted solution, but would give us access to the source code for making changes when needed.
 
Since we cannot get what we really want, we are looking into buying the source code for a reasonably powerful cart that we can modify, as necessary. Would like to have things like cross/up sell; product emails sent on the purchase of individual products, email notification of orders; sales reports; ability to upload/download all products, or at least 1,000 at a time; Good interface with Google Checkout & PayPal; Product search facility; User friendly control panel for processing orders; easy updating of Tracking numbers and status changes to name a few.