I dispise Norton and McAfee products with a passion. They usally cause more problems than they're worth and use up too many system resources. Why waste money buying a program when there are free alternatives that do the same thing.
As for me, I use AVG Antivirus (
free.grisoft.com) and Microsoft Antispyware Beta (Not Defender). They are both free and are very simple to use. They scan my computer at night and update regularly. That's all a security program should do. Oh, and they both do active file scanning, scans files as you use them. AVG also has an email virus agent which will scan incoming and outgoing mail.
Personally, I don't see the need to pay $50 for Norton or McAfee which gets outdated every year when the new version comes out. The two programs I use have never let me down and I've been using AVG for 3 years and Microsoft Antispyware for about 1.