In the past couple weeks, basically since Google acquired Feedburner, there has been quite a bit of chatter about PostRank. Since the Feedburner acquisition wasn’t without issues, the PostRank talk seemed to pick up.
According to their website, PostRank:
… measures audience engagement and provides integrated tools to enable you to customize your RSS subscriptions. Save time, boost productivity, and Read What Matters.
One of the unique things that PostRank does is take into consideration comments and mentions elsewhere on the web (Twitter, Delicious, Magnolia, etc.). It compares it to your recent posts, too. For example, when I first start a blog, getting 1 or 2 comments is a big deal, and thus, will rank that post quite high.