What it seems to do is to look at public subscriptions listed in BlogLines, do a tag analysis, and display a tag cloud. BlogLines is a huge web based aggregator service and so I'd guess that their subscriptions are relatively representative of the whole blogosphere.
In light of my recent musings on bridging the gap between all the great content out there in feed land and regular people, this algorithmic analysis of topics and interest levels is an interesting data point. You can see that the coverage is extremely spotty. I suppose you can draw different conclusions from this:
- The feedosphere doesn't come close to covering the breath of topics of interest that one might have
- BlogLines subscriptions are very caught up in the tech world because that's their user base.
- FeedsThatMatter confuses popularity with value. Perhaps the feeds are out there but , by the BlogLines statistics they don't matter.
I don't know (obviously) which it is...