Ask any bookstore manager or buyer and they will tell you that they do judge books by their covers. In fact, most of the time the only thing they see is the cover to determine whether or not they should carry the title.
Think about your experience. When you are looking at dozens of books on a shelf, how do you decide which one to pick up and read? The cover has to jump out at you or you never give the book a chance.
Even if you are not publishing books, realize you have a brief moment to capture attention. The better you package and present your product, or yourself, the better your odds of someone giving you a chance and finding out more.
What kind of first impression does your product make? What kind of first impression do you make?