Experiments have shown that users can judge a web site’s credibility in as little as 3.42 seconds merely on the basis of its aesthetic appeal.
Recent studies have shown that judgments on web site credibility are 75% based on a web site’s overall aesthetics. [citing Fogg, B.J., Soohoo, C., and Danielson, D. 2002. How Do People Evaluate a Web Site’s Credibility?: Results from a Large Study. Consumer Reports Webwatch. DOI= http://www.consumerwebwatch.org/dynamic/webcredibility-reports-evaluate-abstract.cfm%5D
Farah Alsudani and Matthew Casey: The Effect of Aesthetics on Web Credibility (PDF)