Here's a good article with expert opinions regarding security on Macs vs. PCs: http://news.cnet.com/8301-27080_3-10444561-245.html

Interesting perspectives but nothing really new. I especially liked the part about fleshy humans sitting in front of the monitor who are at fault.

You can't beat a BSD platform in terms of security, stability, and speed but Windows has come a long way. As more and more people use macs, more malware will be developed for macs. The same goes for Linux.

Try PC-BSD http://www.pcbsd.org/

Speaking of "fleshy humans", I had to convince someone just the other day that, although they don't care if they get a virus on their own machine, they're putting their friends and correspondents at risk too. It's easy to see how viruses get spread when so many take this attitude. He even does his banking and business records online and doesn't realize how easy it would be for someone to install spyware on his machine and steal his identity, not just his money. This is a business owner! Yikes!!

Another friend called me up just yesterday to ask which antivirus program I suggested. She said she was "getting a little nervous" running without it, because it expired back in September! Even if you're not using the computer for banking information and bill-paying, you still run the risk to lose all your documents and photos with some of the nastier viruses.

Tom, correct me if I'm wrong, but isn't it difficult to get programs that run on PC-BSD and Ubuntu? Is it difficult to replace OSX or Windows on existing machines? Do you have to start over or can you use existing data from MS Office, iPhoto, etc?

You can install any of the operating systems on a PC or mac. To use a windows application on one of the Linux, BSD, or mac distros, you will need to install some type of virtualization software like parallels or similar.