With absolute respect to Vinh, I've been running Macs sans anti malware since 2004 and never had a problem. I've had to crack open Terminal twice to solve problems that the GUI couldn't solve twice. I have heard the BS that "once OS X gets popular, there will be viruses for it" for years. Anyone want to jog my memory on a real virus for OS X sans cross platform Java exploits and silly disguised scripts that you still have to run as root?
OS X is POSIX compliant, Linux is POSIX compliant. The argument that "once OS X gets popular, there will be viruses for it" could very easily be applied to Linux since Linux runs so many enterprise sites and therefore is popular yet seemingly less affected by malware by an order of magnitude than Windows.
OS X has been steadily growing in popularity yet viruses affecting it have not affected it despite said popularity.
My household is 50% android, 50% OS X.