Check out the link ("The Sorry State of Blog Search Engines") from the Agency Wire site.

I found myself agreeing with much of what the author stated ... that is, blog search simply isn't that good. There is opportunity for some company to improve upon this, but thus far, no company has distinguished themselves. I have hopes for Twingly, and of course Google could always surprise us ... but I just want a search engine that indexes the content, offers me multiple methods of finding AND analyzing said content. Simple!