Since the late 2006 when I started moving to Akismet for some spam protection for this blog, it has already blocked around 930,000 spam comments. Automattic released the latest Akismet stats per blog which is accessible in the WP admin panel.
For this blog alone, Akismet had 936,274 spams caught with 31,680 legitimate comments. That’s and an overall accuracy rate of 99.862%. That’s a really good accuracy but even dealing with the remaining 0.138% of the spam has been already tedious. Had it not been with Akismet and other plugins like Spam Karma, blogs would suffer spam fatigue.
If you look at the rate of spam attack, they range from about 1,000 to 3,000 a day.
There’s also the problem with false-positives.
Spammers always find ways to go around and circumvent the system. And since Akismet is a centralized system, the worst they could do is attack the “central nervous system” itself and the whole thing breaks down (hack, DDOS attacks, etc). I’m fairly certain there have been numerous attempts at this in the past.
There must be some way to decentralize this to avoid that possible catastrophe or every WordPress blog would go down in flames when that happens.