I just deleted my 30,000th comment spam. I have no idea how high the count would have been had I not put into place several techniques that automatically block bad commenters. Those that fall into my traps don’t even get entered into the Akismet system, and so aren’t counted.
(Addendum 9:32pm: The count is now up to 30,447. That comes to one new spam comment every 63 seconds.)