Hi Erik,
I'm a long-time Mac user and currently run five Macs for various tasks. Most of my friends are Mac users as well, though several use Windows or use both (and a couple use Linux). That being said, while we will likely need anti-virus software someday, I don't use any nor do any of my Mac-using friends. There have been no damaging viruses for the Mac in the wild to date, so the inconveniences that come with such software are just not justified for many (or most?) of us. You can visit boards like MacFixIt.com and I think you'll find similar sentiments.
I would recommend spending efforts on a comprehensive backup strategy first, and keep your ears and eyes open for the time when you might want to add an anti-virus layer.
If you are using your Mac to boot into Windows via Bootcamp, Parallels or similar software, then please remember that you must protect your machine from Windows viruses just as you would any dedicated Windows machine.
Hope this helps.
Dale
edit: typo