This is a pretty interesting study: McAfee looked into the different search engines and the result to often used searches. There they checked the safety of the site that was referred (e.g. the presence of malware etc.). You shoudl read their study yourself but here is their conclusion:

It's a jungle out there. Users should be careful where they go and what they do when choosing sites based on search engine results. Despite search engines' efforts, we see too many sites trying to deceive unsuspecting users. These tricky sites span a range of content areas, keywords, and business models – so there is no simple advice as to how to stay safe. Users can't count on search engines to protect them; to the contrary, we find that search result rankings often do not reflect site safety. Users are at especially high risk when visiting search engine advertisers -- even though search engines are well equipped to impose strict guidelines on sites buying prominent placement.

You can read the whole study here: http://www.siteadvisor.com/studies/search_safety_may2006.html

Roger