Marketing Sherpa recently published a very good article regarding the importance of user testing
Their article Top Three Usability Tests for Web Site Redesign Decisions can be found at http://www.marketingsherpa.com/sample.cfm?contentID=3239
Why do users interact with your website the way they do?
The answer to why users behave in a certain way cannot be clearly answered solely by performing a/b or multivariate testing, or by web analytics. This article reiterates the importance of user testing in the design process as user testing can give the design group important insights into why user are choosing to behave in a certain way.
User testing doesn't have to be a huge, complicated and expensive process. That being said, to a certain degree you do get what you pay for, but any user testing is better than no user testing.