Call me a twit but this looks like the place for an intelligent answer...
Most of the time, I find, when people are looking for an e-commerce system they are also looking for cms. Ie. They want to take full control of their site (within reason). I am a designer, a long way from a programmer and I'd like to provide such a service. Design the structure and layout of the site then allow the user to keep it up to date (latest news, latest products etc) I'll get to the question; Do most e-commerce systems provide the ability to create (admin) and edit (user/client) additional pages such as 'About Us' etc etc?? Or do you have to use a cms and seperate e-com solution side by side?
Also, it seems to me, only from reading so far that Cubecart could be the one to tackle since simplicity seems to be it's strongest attribute. Why can't they all be as simple as installing WordPress?!
I'm waiting for Expression Engine to release their own commerce module because I am sure it will be fantastic. It seems the latest commerce releases that keep coming out are usually better and better with time. I've used OSCommerce at first (which sucked!) and now X-Cart (which is a file directory nightmare) so something that is out of the box and customizable with little code is the next best thing. Too bad we have to wait...*sigh*