bislang noch kein mittel gegen spam im blog gefunden.
ich probier jetzt hashcash:
http://dev.wp-plugins.org/browser/wp-hashcash/trunk/
http://elliottback.com/wp/archives/2004/11/29/spam-stopgap-extreme/

By embedding a random hidden field, and then forcing users to compute an md5 hash of that field and submit it back to the server, we stop spam bots. Valid XHTML, requires Javascript. Supports advanced logging and email notification. 100% effective!!

[via wordpress codex, dem neuen user-doku wiki von wp]