We've had our Mac since 2007 and have never put any scanners on here
No offense, but that's dumb as hell.
Yes, it is true that Mac's are less likely to get a virus (due to a smaller user base, so less reason to target) - but they do still get them. Not all viruses/spyware will make a noticeable difference to your machines performance. You won't always get slow downs or bizarre behaviour, files dissapearing/corrupting etc, there are plenty of things like keyloggers which will be virtually silent and cause plenty of harm. Having no scanner/protection at all is a very silly thing to do. You cannot say "You don't
have to worry about viruses" EVER, and you have no way of knowing if you are compromised at all. Personally I've never had a virus on windows using windows firewall and avast (which is free) either - I still keep an eye on it though and those are there to prevent. If I didn't have them, I could just as easily say I've not had a virus and actually have 50 of them lurking on my hard drive because I simply wouldn't know.
As for Mac vs PC, people often compare it as Mac OSX vs Windows which isn't the case at all. For a start there is also Linux, but a PC is the machine not the software. I wouldn't buy a Mac for a few reasons myself, one being that I do regularly play games, and another being that I have over the years frequently upgraded my machine - having the entire thing as one unit is very troublesome. If my monitor breaks I buy a new one, if that happened on a Mac I lose the entire thing until I can fix/replace it. Never seen the obsession with it being all white and super thin either. We had Mac's at Uni in our 2nd year and I much preferred the Linux machines we had in the 1st year, or my home PC. Even when it comes to OS, I like Windows 7 too and never cared for the look of OSX.
I've always found Mac lovers that I have encountered to be similar to Nintendo fans... they are obsessed and rarely accept the existance of alternatives or the idea that their love could do wrong. The amount of "Fck Windows!" rage I've seen from people when the problem they are having is user error is not on the low side. The almost evangelical view they get of it does not help endear me.