Two of the bigger ones: 1) if you're using a popular CMS platform, ELIMINATE ALL FOOTPRINTS. Change all url strings from the default, remove standard text/desc

Two of the bigger ones: 1) if you're using a popular CMS platform, ELIMINATE ALL FOOTPRINTS. Change all url strings from the default, remove standard text/descriptions on signup and comment forms. Kill anything that can be scraped against the rest of the installs to hide your own sites from the scrapers the spammers use to find you. 2) Tap into distributed spam prevention systems. Akismet is probably the most popular example. Your single site will most likely miss the indicators of a spammer, but a system like Akismet can see the 10000 links all pointing to the same url in one hour and lock things down for you. I've legitimately thought about doing a talk at a Wordcamp one day called "How I Spam You" that just walks people through how to spam wordpress, so they can then go protect their sites.