Jeff the difference between backups and VMs are that a VM is typically a copy of the current state of your machine, where a backup is a collective copy of individual files that make up your machine. If you are infected and you don’t know when you got infected you should need the ability to incrementally go back and find a VM that isn’t infected anymore and that copy may not have the file you want that was in another copy.
VM’s are great sandbox tools, the ability to do stuff and get it so messed up that you can easily restore a safe image and start again.
As for not running any Anti-Virus software at all. That’s making the assumption that “you” will be the only one that is allowing your machine to get infected. There is this little thing called the OS that on it’s own allows things to exploit it and get infected.
Take this, albeit far feached thought, for example. Let’s say I was able to hack into or work at a DVR company (like Tivo) and insert a virus/trojan into the next OS of the DVR. Your DVR connects up to the mothership, downloads it’s marching orders and then spends all day behind your firewall trying to hack your pc or futuristic toaster, since you leave both plugged in and/or on all day. So you come home and the only thing you immediately notice is that only half your heating coils work in your toaster. Then weeks or months later, your system eats itself. Then what?
I totally agree that Anti-Virus software is the biggest plight on performance that I have ever seen. However when I am doing things that require all my system resources (like gaming), I just temporarily disable the anti-virus software… And the sidebar, and windows defender… and the firewall… and Windows Update… etc
But when an OS is not a security threat, and it’s left soley up to the user to be a good citizen, then I will be right there with you with my ‘user’ security, no anti-virus and my firewire5000 backups.