Comment spam has got the better of me
My apologies if you're seeing any of my old posts reappear as if freshly published. Comment spam has gotten so bad on some posts that I'm resorting to disabling comments completely. I think this triggers a republish by Community Server (at least, I have to click the "Publish" button), which some blog readers will then interpret as a new post.
If I was sufficiently interested I'd see if there's a direct correlation between the spam-attractiveness of a blog post and its Google PageRank...