Your web site either gives me the information I need easily and professionally or it devalues your brand. Period, end of story.
Is this fair? Absolutely not. You may sell a fabulous product or be an excellent service provider, but if your web site doesn't showcase that really, really well, I am likely to move on to one of your competitors. It's the old "judging a book by its cover" cliche -- we all do it to one degree or another, but in an information culture, the way you lay out that information on my screen is a huge part of how I'll judge your business. People involved in the business of laying out information -- marketing people, graphic designers, people in advertising -- are perhaps more likely than others to dismiss your brand based on how you present it online, but to a lesser degree, all people have a tendency to compare you to the best presentation of similar information they can find.
There are several things that will delegitimize your site on looks alone.