Ben Edelman has worked with the Siteadvisor folks on a fascinating study on the safety of search engines.
Our most notable result? Search engine ads are a risky business. Overall, across all keywords and search engines, 8.5% of sponsored results were "red" or "yellow" by SiteAdvisor's standards, versus only 3.1% of organic results. It's not unusual to see ads for notorious spyware vendors like Direct Revenue (as documented in my January piece); for sites that charge for software available elsewhere for free (like the ad shown at right, trying to charge $29 for Skype's free phone); and for spammers that send hundreds of mesages per week, if a user enters a single email address. These scams deceive and harm search engine users, and I'd like to see Google update its advertising editorial guidelines to prohibit such practices -- then enforce these rules with appropriate diligence.