Netcraft has released a version of their anti-phishing toolbar for Firefox. The toolbar ranks web sites based on a number of factors including age and reports of abuse and displays a "risk bar." I installed it last week and was gleefully anticipating a phishing email to test it out. Naturally, my wait wasn't long. Clicking on the link in the mail took me to a warning dialog box warning me that the site might be a phishing site and asking if I wanted to continue. I declined and was taken to a Netcraft splash page.
I'll probably uninstall it since I'm not all that worried about falling for a phishing scam, but I might install it on my Mom's browser.