I have been working with the centralized comment spam prevention idea for some time and I have a service ready to be tested. It is in the alpha stages of development but the focus is on a simplified interface, incredibly simple installation and ZERO maintenance.
Now a lot of developers and blog gurus poo poo the centralized idea since any central system WILL be vulnerable. However, if centralization itself is distributed, that is, if a hundred people can provide spam protection for a hundred thousand, the vulnerability becomes less of a problem. In the present incarnation of this service, you install a WordPress (various other tools planned) plugin and enable it. Everything else is taken care of for you. The service learns from itself and the more spam you send its way, the better it gets.
Lots of features are planned and some are already implemented. What I am looking for are about a hundred alpha testers with the worst comment spam symptoms. During the testing period things might break horribly (well not really, just comments will be snafu’ed), and you might have to endure frequent updates, but you might very well be free of comment spam, and in the process help create something useful (and make me happy!).
So if Cialis and Viagra haunt you in your morning coffee or if you do not care for the texas-holdem person, (and are willing to be a blog guinea pig), leave a comment here with your blog name and email address (never visible) and I will send you the download link.
If you are a developer with a blog tool beside WordPress (or even a WP hack/dev) and would like to see the insides of the web service, let me know.
[EDIT]: There are no dangers really. If this plugin somehow stops responding and visitors cannot comment on your blog, you would have to manually turn off the plugin (and enable any other comment spam system you might have) Thats all.