I love the design; it's very easy to read, and the simplicity and color make it easy to digest information at a glance.

My constructive criticism:

For the word frequency charts at the top of the screen, I'd weed out common words, and/or try to combine words into meaningful phrases. http://www.wordle.net/ does a good job with this (weeding out common words, not discerning phrases).

The number one thing I think people would be interested in would be some kind of sentiment analysis. Perhaps a knowledgable HN'er could suggest a service you could use for this?

From a UX perspective, I'd like the ability to pause and rewind the twitter streams, or filter them for specific words, phrases, geographic locations, or demographics.

One final nitpick, I would suggest using image meta-tags for sharing on Facebook. I posted the live.votizen.com page to my timeline, and there was no image to accompany the link. Here are the meta-tags you can use for richer sharing: http://davidwalsh.name/facebook-meta-tags

But yes, overall, I love this.