I've recently started using Twitter. Most of the people I follow are bloggers. What do most of them Twitter about? Their blogs! The updates I read look like this: "I have a new blog post." That's all they do!
Guys and gals, I already read your blogs. That's how I know you. I don't need to be told that you have a new blog post up. I'll see it at your blog.
I thought people would do something else with Twitter. Perhaps posting a link or two to something that's not on-topic for one's blog, but that is nonetheless interesting; or something that is interesting but not worth a full blog post. A couple of Twitter-bloggers do this. One famous law blogger is into ballroom dancing. I enjoy seeing his links to various videos. It broadens my world.
But just posting updates that your blog has been updated? That makes Twitter seem like a redunancy.