Point-of-Order Customer-Support Issues
In most instances, the actions taken by the customer at point-of-order are simply selecting the products they wish to purchase and providing shipping and billing information. In traditional transactions, a great deal of attention is paid to the customer's entire in-store experience: from the moment they arrive to the moment they depart, so it's surprising that so little attention has been paid to the online equivalent.
In a sense, these processes should be as straightforward and unobtrusive as possible: the customer should quickly and easily collect the items they wish to purchase and complete the transaction with minimal effort.
He speaks a bit about a "good" shopping cart: which makes it easy to add items and alter or remove ones that have been added previously. Note that making items easy to remove seems contrary to commercial motivations, but attempts to make this difficult are not tolerable to customers. Also, an often-overlooked feature is that a shopping cart should contain ample information for customers to recognize the content (not just part numbers).
Some personalization can be done: you can review the customer's previous order history to discover opportunities to remind or inform the customer when they are expected to want additional items. You can also customize the entire site experience based on this, or give customers the ability to set "preferences" that will make the store easier for them to use.
There is also some power in providing information that has nothing to do with merchandise on sale, but which would be of interest to potential customers. The obvious example is a sports retailer providing information about the sports whose supplies he sells, or a grocer providing recipes for ingredients he'd like to move.