It's great to see that DreamHost added WordPress to the 'goodies'. I've been using it for several months, and am rather pleased with it. However, a month or so ago, I finally fell prey to blog spam--over 120 spammed comments in one day. And they just keep coming.
I would highly recommend installing Blacklist . The link is directly to the zip file for the plug-in. It takes a little bit to figure out the configuration, but it does an excellent job of catching the spammed comments and deleting them.
It's well worth the time to install and configure.
(I have no affiliation with the product or it's maker, I'm just one very satisfied user).