Google recently launched a tool that will help users search for blogs on any topic: Google Blog Search, at http://blogsearch.google.com/. According to Google, the goal of Blog Search is to include every blog that publishes a site feed (either RSS or Atom).
After a search, Blog Search indexes blogs by their site feeds, which will be checked frequently for new content. This means that Blog Search results for a given blog will update with new content much faster than standard web searches. Also, because of the structured data within site feeds, it is possible to find precise posts and date ranges with great accuracy.
In the service's Help section, Google explains:
"Just type the word(s) you want to search for in the text box and click "Search." That's all there is to it! If you want more control over your search, click the "Advanced Search" link to the right of the search button. There you'll find options to specify titles, authors, languages and more. Once you get your search results, there will be an additional link that allows you to switch between displaying the results with either the most relevant or recent results at the top."
Try it out: www.blogsearch.google.com.