An other recently featured thread at WebmasterWorld is named What Can I do about Blog, Forum, and Community Spam? Spam in blogs, forums, and other types of online communities is exponentially getting worse. Heck, I even turned off and disabled completely the commenting and trackbacks ability a couple days ago. I now required people to go to our forum to comment. Why? Because the spam was getting so bad, that it was greatly affecting the performance of accessing the site and also affecting other applications. I disabled it, and presto, we are back in business.
So what can community Webmasters do? - Well, they can take an extreme and turn of blog comments and blog trackbacks, like I did - Require registration - Have active moderators - Use captchas - Disallow or flag certain regions via geo-detection - Use throttle limits
What is interesting, one person claims they blocked certain geo regions and noticed a 2 percent drop in traffic, but a 95% drop in spam.
More ideas in this members only section at WebmasterWorld.