I have been using Windows 7 here for my gaming rig. I am so used to OSX and just doing what I want I forgot I was on Windows as W7 does work very nice. Well I have been hit 4x now with Malware and one true self installing virus. One came straight from a known Disk Utility application right off their server and installed so many nasties it took me 45 min to get rid of them all! Oh well, makes me appreciate OSX more I guess!
A note to the OP, I am not careful on OSX, not at all and do what I want. Only care I take is putting in my password when asked for a download until I am sure what it is. Otherwise I go all out. Am sort of a Hacker type. Never once in around 10 years now have I ever been hit. I had to go find that DNS re-director Trojan and force it to install just to see it work. It took me 30 seconds in the terminal to remove it. So do not worry too much about AV. Just use your head and do not give access to anything you don't for sure know what it is and you should be fine.
Let the flames come. Facts are facts.