From ARS Technica:
Clickstream data includes every web site visited by each user and in which order they were clicked.The data is not sold with accompanying user name or information, but merely as a numerical user value. However, it is still theoretically possible to tie this information to a specific ISP account. Cancel told Ars that his company licenses the data from ISPs for millions of dollars. He did not give a specific figure about what this broke down to in terms of dollars per ISP user, although someone in the audience estimated that it was in the range of 40¢ per user per month
Bookmarks