A non-techie IM friend is feeling a bit confused between Google Blog Search and Google Web Search engine.
His argument - when Google Web Search indexes blogs as well as millions of other webpages that are not blogs - why should one use a blog search engine ?
Well, there are least five differences between Websearch and Blog search engines listed below: [If you can think of more reason, please put them in the comments]
1: A web search engine indexes Blogs, Webpages, Forums, PDFs and even Microsoft Office Documents. Blog Search Engines index only sites that syndicate content as a feed in either RSS or Atom formats.
2. Blog Search Engine bots will index your website as soon as you ping them (or notify them about new content on your blog). Search engines spiders are much more lazy (unless you are a PR8 or PR9 website) Infact, it's not even guaranteed that a search engine would index your site.
3. Since XML feeds supply data in a more structured format to the blog search engine, you can sort blog search results either by date or relevance. In normal web search engines, results are sorted by page relevance since their bots do not know the exact date when the article was written or published on the web.
4. Web Search engines index all parts of your webpage including reader comments, text in the sidebars, etc. On the other hand, most blog search engines index just the text of the blog post that was supplied to them inside the RSS feed. They won't index other elements of the webpage like Archive links, Blogroll, etc.
5. Blog Search engines let you restrict the search to a particular author, something not possible with Web Search.
Summary: Use a blog search engine when you need information about an event that happened just seconds ago like someone smashed his PS3 on the road.
In all other cases, you may prefer using a web search engine.