Usability reviews are great for existing websites, especially ones that weren't built using sound information architecture.
Consider this scenario: you just spent thousands of dollars on pay-per-click (PPC) campaigns in order to drive thousands of potential customers to your banana ice cream website. Then when customers got to your website, they couldn't figure out how to get to the order form. Bummer.
The purpose of a usability review is to give you the information about what you need to change in your website in order to avoid user problems. It tells you how to make your website conform to web standards and not be confusing to use.
Even though the web as a medium is only little over ten years old, a whole set of web standards have emerged. Keep navigation links in a typical place, put the site's logo in the top left corner, don't make text a light color on a light background.
Following usability rules keeps websites familiar to users and levels the learning curve to no curve at all.
Let Crunch42 Web Services conduct a usability review for your website so you'll know if you're losing customers needlessly, and what exact steps you need to take in order to win them back.