Technorati

Technorati is an Internet search engine for searching blogs and social media.
According to the company, they are currently" tracking 112.8 million blogs and over 250 million pieces of tagged social media."

When bloggers link to and comment on other blogs, Technorati tracks these links. Technorati indexes thousands of updates every hour.

According to Technorati data, there are over 175,000 new blogs (that’s just blogs) every day. Bloggers update their blogs regularly to the tune of over 1.6 million posts per day, or over 18 updates a second.

Technorati gives blogs an authority rating, based on how many other blogs currently link to it. About two-thirds of the information that is currently discovered by Technorati users is through tags. The rest comes from keyword searches. A December survey by the Pew Internet & American Life Project found that 28 percent of Internet users have tagged content online such as photos, news stories or blog posts.