I was using Norton's but declined to renew the subscription (I got it cheap when I bought a new PC last year), not least because I was fed up of having to wait about 10 minutes when I booted up for it to finish its scan and let me actually do anything!
A colleague at work was having problems with his home PC and thought he may have a virus (he wasn't using any AV software). He ran a virus & malware checker and was informed there were a few thousand suspect files!
I also sorted out a friend's PC a few years ago, and that had shedloads of malware on it!