I was cleaning up posts, but I didn't realize that "Update" would update the original date of the post.
So instead, you all got spammed with about 80 updated posts from last year!
Yikes. And of course, I don't know the original post dates, so I can't go and fix them... Argh. Will have to see what I can do.
Update: Oh good, it seems that tags didn't update the post dates, just the cases where I modified the actual post text. So just a few posts that appear today but were posted ages ago.