Stir it up - News Mixer
An interesting Open Source CMS project that tries to reinvent the news website.
The problem I have with some of the features (twitter like comments, and per paragraph comments) is when you give people too many options on how to comment, then they might not comment at all.
I can see the would-be commenters thought process now: "is my comment important enough to be a letter-to-the-editor? Or should I just leave a normal comment? Well, it might be more of an observation than a comment, so maybe I should leave a quick twitter like blurb." Then, on finally deciding to leave a normal comment, our would be commenter has to decide on which paragraph to leave the comment on, or on the whole article.
I first saw per paragraph comments in 2004ish, it was on the blog of a Yahoo developer as a proof of concept. I thought it was cool then but 5 years later it still hasn't caught on and I think it is because nobody wants to mess with a formula that works: "have a question, comment, observation? Write it below." rather than: "leave a comment below, but if you have a question, leave it on the paragraph, but if you have quick observation, then why don't you leave it on the side."
Less is more people.
Here is another writeup on the Newsmixer code.