I'm still not entirely convinced of the benefits of twitter, though it's quite fun to announce to the world that you're about to catch a bus or thinking about the weekend. Some twitterers (or is that tweeters?) provide streams of interesting links and info. One of the best on digital publishing is Jose Afonso Furtado in Lisboa Portugal,
teaching a post-graduate course on "Books and Publishing in Digital Era" at Universidade Católica de Lisboa - and churning out masses of links to interesting things.
You can find him at http://twitter.com/jafurtado.