E-commerce sites want to "engage" with their customers, but fail to realise that the customers don't want a relationship. They just want whatever product you're selling as quickly and cheaply as possible. Most of you customers will be coming via price comparison sites or Google, so they aren't going to you directly (unless you're Amazon or eBay). For most e-commerce sites the customers aren't going to stay long enough to notice imperfections in the UI.
What you do need is a dead simple checkout (no signup required) and an equally easy return form. Everything else will be used by only a tiny percentage of your customers, often those you don't want to deal with anyway.
For some weird reason making the checkout to simply will result in a large number of purchases cancelled right after placement. In my experience customers are more likely to cancel within 15 minutes of placing the order than at any other time.