What does it have?
- Search through feeds (too bad for those blogs expose none or partial feeds).
- Google's trademark simplicity.
- Search logic -- just like the other Google searches.
- Search result as Atom or RSS feed.
- And FAST.
It seems to return very recent entries. When I searched for google "blog search", ordered by date, the most recent entry was posted only 27 minutes ago! I can almost hear server boxes in Google's data centre spinning as fast as it can, grabbing all the blog feeds it can possibly find, feeding them into the busy working indexer and making them available as part of the SERPs.
Talking about speed, it is definitely a noticeable improvement over Feedster and Technorati, two of other feed search sites that I frequently use. Actually, this morning the speed on the used-to-be-sooooo-slow Technorati was actually not too bad, probably as many blog searchers have migrated to Google Blog Search to find their niches.
Quality and relevance of the search is about the same as the quality of many blogsites out there, but I guess the difference between a feed search and a regular page search is, relevance is considered less important than how frequent new entries are added into the index. People come here to find out what is the latest, but not necessary the solutions for their problems.
However, Google Blog Search still lacks many useful functions that are available on Technorati. So far Google has only built a great search engine for blogs, but Technorati has built a "community" for bloggers, through easily accessible back-links, blog profiles, and folksonomy via tagging/categorising.
Again, Google Blog Search is only in beta, and I believe there will be much more to come. Google has released its product early to the public, telling its competitors -- hey! Watch out! And surely they should.