As for anti-virus, I have been using the mac for nearly 10 years, and I have never installed anti-virus nor have I had any problems. Part of it is that there isn't as much to gain by exploiting macs (fewer numbers), but I think the general security model for unix was very mature when script kiddies started exploiting windows back in the late 90s, making anti-virus necessary. All you needed to know back then was basic, and you could write yourself a melissa virus that took down whole companies for days. 

10 years without an anti-virus program.   I never really understood how people without antivirus claim that their computer doesn't have a virus or could never get one.  Even worse you state that there isn't as much to gain by exploiting Macs.  Mac users have credit cards and bank accounts just like everyone else.  A target is a target regardless of what OS they are running,  The fact that many Mac users don't use antivirus software or firewall software makes you an easier target. Here's an article from 2012 Malware Infects One In Five Mac Devices: REPORT   The top malware problems that affect Macs comes from flash, but only Macs have that issue. According to the report, PC computers don't have this same issue.  In addition the report states that Mac leads the OS world for having security vulnerabilities.  I can only assume that Mac users who think their computers don't need antivirus or firewall software would have the most security vulnerabilities.

I clean malware off of computers and the majority of the malware and viruses that I find don't cause problems and the only way that anyone would know that they are there is to run a software that can detect it.  Just something to think about.