To me there are different philosophy of using twitter. Indeed some people use it to broadcast their everyday life. But there is also a large number of people using it as an information broadcaster.
The people I follow are usually experts on some topics I'm interested in and I use them as filter to get word of lots of information which could have a hard time to reach me otherwise.
I myself do the same, when I find out some interesting information which corresponds to the topics I usually talk about, then I broadcast it. That way my discoveries (small and on some very focused topics) ended twice in the website of one of the biggest french newspaper (lemonde.fr). How it ended there is because a journalist of a smaller website follows me, he read it, and published an article. This article was then used as a source for lemonde.fr
The other point of twitter is conversation. It is much more horizontal than in the real world (maybe because unlike email people feel less obligated to reply, so in return they reply more). With twitter, I have been able to exchange with some people I wouldn't be able to otherwise (I don't live in a big city, those people aren't from my social circle, but we share some common interests).