(http://www.goodexperience.com/blog/archives/000223.php) about some results of an evaluation of some common ecommerce web sites. Here are the general problems they found:
1. Content groupings that reflect the company's view of the business, not the customer's view.
I don't know why this is still a problem. We have known for years it is bad design. My undergrad students figure it out by week 3. For some great proof, check out Julian Sanchez' masters thesis at Florida International University.
2. Navigation that hides important categories
Here is another no-brainer. If there is content that people want to see, why hide it? Make it salient !!
3. Confusing product images
I suspect that this one is as much about poor marketing as it is poor usability. If companies either rush to get their photos out there, or don't invest in good technology, the images won't do what they are supposed to do, which is clearly to support product evaluation. If the customer can't tell what the product looks like (stylistically or functionality), then how do they know if they should buy it? The specs for the image should be pretty easy to figure out and test.
4. Missing product information
This is the same issue as #3. Analyze the customers' decision making processes (there will be many) and make available any information that they need. I have debated with Eric Goldman (a marketing professor at Marquette University) about whether we give them the information they think they want, or just the information that would really help them make a better decision. He is very sure it should be latter. I agree to some extent, but customer satisfaction increases with the former.
5. Important information not being presented at contextually relevant points in the process
Strangely enough, this one I understand. It is difficult to know the decision making processes of the customer, primarily because they are all different. Some will want to filter on price first, but others will filter on price last. So when do you present it? The trick is to be flexible. Let the customer decide in real time (using dynamic page design and product databases) what data to access.
6. Difficult product-comparison functions
This one is partly a lack of human factors expertise, and partly a love of complex technology that looks cool. Many companies don't realize how important human factors is in product comparison. They either put huge tables of data that are hard to parse, or they have each product separately and require customers to pogo stick (see Jared Spool's work with UIE) up and down the hierarchy to read it all.
So in the end, it just comes down to using a good design process, understanding your customers' cognitive processes, and testing, testing, testing.