
@ the people not using any antivirus
it's just like having sex with random people without a condom. Seriously, even if you "pull out" and play it as smart as you can you're going to get infected or end up with a child draining the life out of you eventually.
All it takes is to click one link of a site that looks legit - hell, even a site that is legit. Microsoft.com has been hacked in the past (Ok, not the best example because their security is...) and if the hackers wanted, they could've infected thousands of people just visiting microsoft.com. You don't have to download anything to get infected, either.
Anyway back to my condom analogy, lots of men don't wear them for the reason "it doesn't feel as good", whereas with an antivirus.. why wouldn't you be running one? They're free, no hassle, and most use very little system resources.
The only reason I can think of for not having one.. is to brag on forums that you're too smart to get a virus? (Please give me another reason, I'd love to hear it, I'm not being sarcastic.) Sorry to break it to you, but no, you aren't. There's always someone smarter and with less of a life than you taking his revenge out on the world through the internet.
edit; this really only applies to people running Windows based machines, I don't believe there are any documented cases of virii on a Mac or Unix based OS. yet.