Oh, stop. FlwrPwer is almost right - the malware quotient for OSX is low because of low adoption figures and malware authors want high ROI like everyone else. But to draw a line to a low RISK of vulnerability is a scary one. That's like saying that the US is not vulnerable to terrorism because we haven't had an incident since 9/11 - the abscence of something does not prove that it does not exist.
The fact is that vulnerabilities in OSX have existed, been exploited, and have been patched, and that cycle is likely to continue as it does with other operating systems. Google "OSX vulnerability" and read a while, and you'll realize that if anything, you have security by obscurity.
Here's just one link to read:
http://www.eweek.com/c/a/Apple/Apple...al-OS-X-Flaws/