Every day starts with a depressing routine of adding 4-8 new spam URLs to my blacklist.
Yes, there are distributed blacklists like Akismet.
In terms of how many are active, 7.5 million blogs have added a new post during the last four months, and 1.5 million have been updated during the last week.
After you publish your post, you send a trackback to my post.
This is usually handled automatically by the blogging software. I get notified of any trackbacks to my posts, so I can follow the trackback to read your response.
Trackbacks, as a result of Six Apart's incredibly naive initial design, are now a total loss.
That's what happens when you design social software without considering the impact of malicious users from the very beginning.