Most definitely yet. Twitter search has some real potential. It's growing rapidly as a place that people can search for quick reviews of restaurants, movies, etc.
This makes no sense. Why would I use twitter to look for reviews on restaurants instead of Yelp? Why would I use Twitter for movie reviews over metacritic or rotten tomatoes? Hell, if I'm going to use search to look for reviews on something, why wouldn't I just use Google?
And one thing that is interesting about this is that Google is a superset of twitter, and twitter could never be a superset of Google. Google can more easily index twitter's content than twitter could index the rest of the internet.
Despite the question "What are you doing right now?", the value in Twitter is that people answer "What are you thinking right now?" I can use Twitter search to find some things out faster because people's opinions appear on Twitter before they appear on Google.
This is not to say that Twitter will replace Google. No way, this is an entirely different problem. The reason Twitter search makes sense is that it takes the search problem one step forward towards a recommendation problem. With Twitter I can get real opinions from real people. It's not that I can't do that with Google. It's that Twitter is a little faster and a little better.
If I was unclear and suggested that Twitter should become a search engine or acquire a search engine, I apologize. If anything, a search engine might want to consider acquiring Twitter.