Dave Sifry of Technorati does his numbers dance: Technorati is tracking 18.9 million blogs. The pattern remains: a doubling every five months. A new blog is born every second. 55 percent are posting three months later; 13-15 percent update weekly or more. About 8 percent are spam blogs. There are recent spikes from the creation of Chinese blogs…. Tags are exploding. Almost a third of blog posts use tags or categories, he says…. He’s announcing deals to provide blog links to the Washington Post, IHT, Atlantic, and Der Spigel, on top of Newsweek and Salon…. He’s also announcing a refinement of search to look within given tags (e.g., Bush within only political blogs).