I'm very curious about this...how did they collect their data? Did they spider/screen scrape HN, or were they able to get a data feed/dump?

I've mentioned before that I'm interested in making some better algorithms for social news sites (I'm learning Scheme/Arc so that I can play around with news.arc); I think one very neat feature that could be added to social news sites is a sort of 'tracker' -- just like torrent trackers have a standard URL that clients can reach certain data at, it would be very cool for social news sites to decide on a data format whereby spiders and the like can get data feeds on stories, user "karma" and so forth.

To expand on that, you could even normalize the scores from each site, and build a social news "karma aggregator" that monitors lots of these feeds, and ranks your username across all of the sites!

EDIT: When I get up to speed on Scheme/Arc, I think I'm going to write a 'stats.arc' page to link into news.arc somehow. Is that a feature that anyone else thinks is useful? I'm talking detailed stats analysis/heuristics here, not just the 'top XX users' or whatever.