As I said, twitter is realtime search, something google can't do at the moment. I see google and twitter merging rather than one replacing the other.
Example. If there was a tornado in JHB. You'd simultaneously have 2-3000 people in JHB all sending out tweets with the words "tornado" and "JHB", this would immediately send these 2 words to the top of the trend list, and within seconds, anyone anywhere in the world using twitter would know there's been a Tornado in JHB. (realtime info)
OR,
When the internet is down, a quick search using search.twitter.com will reveal a hundreds of people saying "internet is down in JHB" (realtime search results)
As I keep trying to point out, "Twitter is not so much about what you are saying, it's about what EVERYONE is saying."