I've installed McAfee SiteAdvisor to my home computer and I'm impressed.
In Yahoo or Google search, you can get a preview of the safety rating of the website before you click on the link. If it's good, it will have a check next to it, if not, it will have an "X" or exclamation mark next to it and it will have an explanation of McAfee's findings.
Here's a screenshot! (Yeah, all Chexed related stuff should have green checks ;)
So get to downloading if you want! It doesn't create an extra tool bar, thank God!