I moved LISNews to the ibiblio servers a couple weeks ago, and since I can't mess around with mod_security rules there, I was worried about spam comments. I could see within just a day that the mod_security rules on LISHost were much more restrictive, and had blocked more spam than I thought. At about the same time someone complained about the captcha not working, so I though I might as well try something new, so I installed the Mollom module. "Mollom helps you stop comment spam, contact form spam, forum spam, fake user accounts, etc. To do so, Mollom combines context analysis and accessible CAPTCHAs to optimize your site's accessibility and experience."
So far, so good, I've only had to report one comment as spam so far, and it says it's blocked a ton. Mod_security can be a big huge PITA sometimes, but I can't imagine running a web server without it now. You'd be amazed at how much spam is thrown at every single blog on the LISHost serves.
I'm also more than a little happy with the folks at ibiblio. They've been helpful with a few little problems, and the servers get the job done.