Google has launched Google Blog Search.
On the About page they write that the entries go back to about June 2005. The goal seems to be to include every blog in the world (though only 35 languages are currently supported), that has an RSS or Atom feed, not just those on Blogger. Their coverage seems to be pretty thorough; they have all the ibiblio blogs that I could think of to search for, plus all the library blogs that I could think of that have their own domains (librarian.net, Librarian Avengers, Free Range Librarian, etc.). Most interestingly, they’ve also invented some new search operators: