I sort of remember it being announced, but didn't pay much attention... then again, I'm pretty sure the proposal was only in the hundreds per day, as recently as a few months ago.
I also don't know exactly when the comment-voting side of it began, or if it has always been at this scale. Easy enough to find out of course.
RE: The main excuse for malicious down-voting is "Over-Rewarded Content..." What about the account making $10k+ PER DAY in spam comments?