I just learned that tonight's vice presidential debate will be broadcasted on Current.tv, partnering with Twitter.
While you watch the debate on Current.tv either on cable TV or on the Web, you can send you comment through Twitter and a part of the comments will be displayed on the screen in near-real time. (They say they cannot show all the comments, though.) To participate, you have to have an account with Twitter, and are supposed to add a tag "#current" on your comment to be included.
This "user comments on the screen" style is already common in Japan, with the popular web service called "Nico Nico Douga". The service allow users to comment on the YouTube-like video uploaded by a user. The strength of it is that even though different users are watching the video at different times, you can see the comments synchronized with the video, making you see the comment at exactly where another person make a comment, so it feels like you are watching the video with many other people at the same time.
This time, the debate is the real rea-time, but the concept probably is easy to understand for Japanese net participants. But as always, US does it in bigger scale in major event. Interesting.