There's a few studies that show sub-conscious reactions to the aesthetics of a page are made within 50ms, and that these reactions then impinge on the user's sense of usability, satisfaction, and the credibility of the site.
Attention web designers: You have 50 milliseconds to make a good first impression! (PDF), Lindgaard G., Fernandes G. J., Dudek C. & Brown, J.
Tested subjects by displaying web pages (saved to disk) for 500ms or 50ms for "visual appeal." The report concludes that "...visual appeal can be assessed within 50 msec suggesting that web designers have about 50msec to make a good first impression." Behaviour and Information Technology, 25:115 - 126 (2006).
Web Users Judge Sites in the Blink of an Eye, Hopkin, M.
Nature first reported on the study online on Jan. 13, 2006.
First impressions count for web, BBC News, Jan. 16, 2006
Early news report of the "blink" study after the Nature story. "My colleagues believed it would be impossible to really see anything in less than 500 milliseconds." -- Gitte Lindgaard et al
Carleton University, HOT Lab
Human Oriented Technology Lab at Carleton University in Ottawa, Ontario Canada researches "interactive technologies for human endeavors with an emphasis on human computer interaction and a user-centred design approach." Dr. Gitte Lindgaard and her colleagues work at the HOT Lab.
"A second chance for emotion", Damasio, A. R.
In Cognitive Neuroscience of Emotions edited by R. D. Lane and L. Nadel (New York: Oxford University Press, 2000).
Stanford Guidelines for Web Credibility, Fogg, B.J.
Persuasive Technology Lab. Stanford University, 2002 (revised November 2003). In two surveys of over 2600 people Fogg found that a "clean, professional look" was cited by 46.1% of participants when evaluating sites for web credibility. Information Design/Structure was cited 28.5% of the time, while Information Focus was cited 25.1% of the time. While the factors varied for different types of sites, disguised advertising and popup ads, stale content, broken or uncredible links, difficult navigation, typographic errors, popup ads, and slow or unavailable sites were found to harm credibility the most.
Blink: the power of thinking without thinking, Gladwell, M.
A fascinating book about how accurate our first impressions can be, especially among those with a lifetime of experience (art appraisers for example). (New York: Little, Brown, and Co., 2005)
Response Time: Eight Seconds, Plus or Minus Two, King, A.
In Speed Up Your Site: Web Site Optimization), Indianapolis: New Riders Publishing, 2003. The consensus among HCI researchers is to deliver useful content within 1 to 2 seconds (navigation bar, search form) and your entire page within 8 to 10 seconds (8.6 seconds was the figure most cited).
This article has further reading.
Flow in Web Design, King, A.
In Speed Up Your Site: Web Site Optimization, Indianapolis: New Riders Publishing, 2003. Fast, well-designed sites can actually create a flow state in users. In fact, according to a recent study, over 47% of users have experienced flow on the Web.
The Emotional Brain: The Mysterious Underpinnings of Emotional Life, Ledoux, J.
1996, Simon & Schuster, 1998 Touchstone edition: ISBN 0-684-83659-9
Understanding web browsing behaviors through Weibull analysis of dwell time, Chao Liu, Ryen W. White, and Susan Dumais, 2010.
In Proceedings of the 33rd international ACM SIGIR conference.
Jakob Nielsen provides a good summary of the study, stressing the importance of surviving the first 10 seconds.
The role of visual complexity and prototypicality regarding first impression of websites: Working towards understanding aesthetic judgments, Tuch A.N., Presslaber E, Stoecklin M, Opwis K, Bargas-Avila J; 2012.
This paper experimentally investigates the role of visual complexity (VC) and pro- totypicality (PT) as design factors of websites, shaping users’ first impressions by means of two studies. Results reveal that VC and PT affect participants’ aesthetics ratings within the first 50 ms of exposure. In a second study presentation times were shortened to 17, 33 and 50ms. Results suggest that VC and PT affect aesthetic perception even within 17ms, though the effect of PT is less pronounced than the one of VC. With increasing presentation time the effect of PT becomes as influential as the VC effect.