UPDATE, 3/28/16: Since this was originally posted, Google Kills Blogsearch (Again) - But This Time They REALLY Mean It

Google Blogsearch is no more. It appears that Google has killed the blog only search database.

Requests for the blog-only search interface that used to live at http://google.com/blogsearch and http://blogsearch.google.com now return a "page not found" error or redirect to Google's "regular" Web Search interface.

It is, however, possible to force Google to display the Blogsearch interface and search the Blogsearch database by manually adding the application for the Blogsearch to your the URL in your browser's address bar (or omnibox) - like this http://www.google.com/search?tbm=blg. (tbm instructs the the browser to retrieve a specific application from the Google server and blg is the designation for the Blogsearch. A complete list of Google application designations can be found at http://webapps.stackexchange.com/questions/58550/what-does-tbm-mean-in-google-search.)

Blog results can also still be displayed by clicking the "Search Tools" button above Google News Search results, then clicking the "All News" drop-down menu and selecting "Blogs." However, this list of blog results is not as extensive as those retrieved by searching the above-referenced URL.

For example, retrieving the Blog-only results from a Google News search for the keyword Obama returned results drawn primarily from the blogs of mainstream media news sites (e.g., Washington Post, Wall Street Journal, Fox News) and covers only a date range back about 23 days.

The same search using this interface http://www.google.com/search?tbm=blg returned results from a wider range of blogs (including smaller news outlets and personal blogs), as well as covering a broader date range.

While it would be logical to believe that you could extend the date range of your Blog-only News Search results by creating a "Custom Date Range" (using the "Anytime" drop-down menu), this Custom Date Range does not actually work in the News Search for any dates beyond the News Search's 30 day coverage range. (It is a remnant of the old News Archive Search.)