I've been running Norton Security Suite for about a year. I understand previous versions were a resource hog, but this one is slim and fast.
I like the way it grades Web sites for security risks, but my favorite feature is the frequent (almost minute-by-minute) virus definition updates. Malware can hit the 'net and spread in a matter of hours. If the software updates the virus definitions only every few hours, you could get infected before the next update.