How quickly do you back-button away from a home page that's slow to load?

I know I’m an impatient sort when surfing the Web. Unless I truly need to look at the information on a particular site, if it doesn’t load quickly, I am likely to back button out and try a different site or a different link in the SERPs. I’m sure I am not alone in this behavior. There has to be a curve for the page view loss per millisecond of load time. How many eyeballs does 5 seconds cost a Web developer?

I tried to search Google for actual research that shows the curve of page-view drop off per millisecond of load time for a given set of sites. I wasn’t able to find it. Does anyone have a link to such info? If not, and if you need a great research topic for a Masters or PhD., then doing the research might be a great thesis topic.