Google Real-Time Search: some questions

Google today announced its inevitable reach into real-time search, instantly adding results from Twitter, FriendFeed and MySpace. As cool and useful as this may be, I’ve got a couple of questions about it.

How do they assign relevance to tweets? Google’s search algorithms are based, in large measure, on the number and quality of backlinks — relevant links to a given page. How is Google assigning relevance to tweets? By hashmarks? By the number of followers on an account? That’s obviously problematic, given the triviality of manipulating it. By the number of relevant followers? Then what determines relevance?

Is more weight given to official pronouncements from known or trusted entities? How do the entities get to be known or trusted? And if “official” sites do get preference, isn’t that contrary to the whole idea of Twitter?

What about a common situation where a reporter for a publication tweets about a story that’s about to break on their site or in print? How is that differentiated from an unsubstantiated rumor that some celebrity has died?

It’s not Google’s place to be judging the truth value of tweets or posts, but I worry (as often) that this will only accelerate a race to the bottom.
And one more: Tweets are 140 characters long. Google snippets are 156. By presenting tweets on SERPs, Google is preempting one possible means for Twitter to monetize: ads. Why click through to a Twitter page when you get all you need on Google’s?