The author of the article pretty much has it right.
Linux and Mac don't have nearly the attractiveness windows machines have when it comes to writing virusses. Also, particularly Linux, they are very diverse in setups, installed packages, and versions. This makes a successfull infection a lot less likely to spread very far very quickly.
A user above mentioned that exploits in the kernel may still be found: this is true, and not any less than with MS windows or other OS software, the matter-of-fact is however that Linux and other opensource software have a far greater mean response-time to security breaches than MS. (honestly: I do not have figures to back this up).
Education and diversity are keywords IMHO...
My little security tip for today: protect your network of X-machines by a Y-firewall. I run Windows 2000 but my network is routed through a linux firewall... I never had any risk of getting the sobig.F worm or the like because of this setup. To get to my machine, manual labor has to be done or a dual-os worm has to spread...
(this is not an invitation to crack my firewall or such... I know very well it can be done, and probably quite easily, it does not need to be proven, thank you
)