An interesting study reported at New York Times:
But neither of these is the most valuable kind of Web site visitor. That honor goes to the people who arrive at a site by typing its Web address directly into their browsers or clicking on a bookmark. Such visitors, who tend to be repeat customers, linger the longest, spend the most money, and are the most likely to “convert†to buyers, doing so on 3.3 percent of their visits. On average, their visits are worth $5.69 apiece.