For some reason (I suspect an attempt to get badges), users go to threads as old as one year to reply to them. In light of this, I've added a new rule. I suggest you read it. I also suggest you follow that page, so as to keep yourself up-to-date on any future modifications to the rules.
A bureaucrat has found a piece of code that should take care of this issue, so the rule has been altered. Now it only pertains to talk pages. However, you may experience a significant slowdown on some pages; particularly forum threads and RecentChanges.