Pretty much every site with user generated content is overwhelmed with people trying to post spam. For my site, I use a combination of javascript human detection, bayesian filtering, and aggressive human intervention (including single click "spam this" links on every piece of content when logged in as an Admin)
It's worth noting that since late 2007, a significant portion of comment spam is human powered. CAPTCHA style bot filtering doesn't work against it, since it's not bots doing the posting. Bayesian filtering and good moderation tools are essential these days.
It's worth noting that since late 2007, a significant portion of comment spam is human powered. CAPTCHA style bot filtering doesn't work against it, since it's not bots doing the posting. Bayesian filtering and good moderation tools are essential these days.