The first of Cesar's four rules for when a technology will take off is: "covered in mainstream business publications." Perhaps a related test for when a technology has truly reached the mainstream is: "is the topic of a New York Times editorial."
Today's NYT has an editorial on Measuring the Blogosphere, discussing Technorati's "State of the Blogosphere" report. A few stats: "Nearly 80,000 new blogs are created every day, and there are some 14.2 million in existence already, 55 percent of which remain active. Some 900,000 new blog postings are added every day."