Many people consider the only things that matter when designing a website are looks and search engine optimisation. This is simply not true, people are increasingly impatient and want things now, not in a 5 minutes. With so much choice available on the internet it is becoming so much easier to visitors to buy elsewhere if they can't find your product on the first attempt.
Usability is becoming so much more important for your website. Visitors are increasingly more difficult to get, so once you have them, keep hold of them.