It might be even more interesting to do comparisons between subreddits and comparisons between hashtags or followers of certain figures.
Also do you have a link to the source?
Keep up the good stuff!
I have been thinking about subreddits and hashtags, but I'm not sure what would be interesting to people and still have enough statistical significance to update every half-hour/hour. If I were going to release this on Reddit, I'd have probably arranged it as a comparison between all the major subreddits. As for hashtags, their impermanence makes them a difficult measure.
I don't have the source up yet, but it's pretty simple. I just get the json output of /all/comments and get the Twitter streams for the words I'm checking with ntwitter and then do the basic math to analyze it every half hour. I render the page myself with the backlog of values and then send it updated info as I process it, so if you leave the page open, it should keep fresh.