I haven't run antivirus in 5 or 6 years now and I exclusively run Windows (though I do run Linux in a VM when I need it). Common sense is the best protection against viruses. Run a hardware firewall, keep systems patched, don't click on random email attachments, etc..

  On a side note, one feature of Vista (which gets ignored) is the fact that IE7 runs inside a sandbox. Obviously this doesn't make it impenetrable (e.g. a flash exploit was used recently to gain access outside the sandbox), but this is a great step in making an OS more idiot proof.

 ditto.

 Mac market share in the US is 14%, up 60% from last year. You might want to update your numbers ;)

The Mac is very secure for the same reason Linux is. They are both Unix derivatives, and when talking solid OS's, Linux and Mac OSX should get in the ring and fight. MS should just slowly, quietly, slip out the door and hope no one saw it at the party.

I run avast on my pc. I have never actually run a complete virus scan and its been a year or two since I have run any spyware checks. Maybe I should.

I use a firewall on my PC and the anti-virus scans every email i receive and alerts me with every download.

There is some stuff you should avoid on the net. Keep away from porn that has heaps of viruses, torrent downloads are dodgy as and many viruses are attached within "free" downloads. Downloading music from Lime wire can result in malware or various other viruses.

Chain emails should be avoided like the plague and do not forward those emails on. emails with sussed headings should not be opened. If you do not know the user who send attachments do not open it. 

I thought the mac was the easiest of the three to hack/exploit, as demonstrated earlier this year.

Never, I use OSX

DOS is a UNIX derivative last I checked, and the Windows 9X series uses a DOS base. The biggest difference is that one has a huge market share and the other two don't. I remember when Firefox was supposed to be the ultimate browser with no security issues and then it gained a significant market share and people started exploiting it. Opera, my browser of choice, benefits similarly from security through obscurity. No system is perfect, and people love finding holes to exploit. When the Mac userbase hits big enough market share there will people lining up to exploit the billion vulnerabilities no one knows exist yet.

@Soriku

Tell me AD-Aware isn't your virus "protection." Please tell me that you simply forgot to put your virus scanner. If not, go download AVG and let it do its thing. It is the second best protection against viruses out there. The best by far is users being intelligent and safe on the internets, but that is not something you can guarantee on a family computer.

I sometimes search myself for strange startup programs or registry changes, like a couple of times every month. But I rarely do full scans. I have programs that protect the internals of Windows quite well.

You search YOURSELF for startup programs?