Ok, I'll admit it. I've been living dangerously
for the last several years.
To be blunt: I refused to install any kind of antivirus or personal firewall software on most of my computers (but see Update 1/1/2012, below.) This included a Windows XP Home system that was used by my children as a web surfing / email / game system. I suffered zero infections during this time. (The only time I ever suffered a malware infection was before, when I did rely on Norton Antivirus to protect the kids' computer.)
Why do I refuse to use these
massively popular widely-used products? Simple. I am convinced that in my case, they may cause more harm than good, and that they foster a false sense of security - leading some users to engage in riskier behavior.
Further, antivirus software is almost always behind the curve - by definition, the antivirus people are playing catch-up with the malware writers. It's a good living for them, but I choose not to contribute to it.
As a software developer, I cannot afford any downtime due to buggy software, and yes - antivirus software has bugs. Not long ago, one major antivirus package ran amok, causing widespread damage by deleting harmless user data and programs.