viruses and spyware are not mutually exclusive IMO. Spyware is worse because it could leak private info not just mess up your comp. My uncle needed help getting rid of something that told him he had a virus... it took over the whole screen every 10 minutes and prompted him to pay to fix the problem. Wouldn't let him run antiviruses or ctrl alt delete, ransom ware is what it's called. somehow got it 4 hours after opening the box to his computer ;>>. the best viruses/spyware try their hardest to make sure you don't notice them. So not seeing any indication of something isn't saying much.
Macs will get viruses as soon as the market share gets higher. It's not that they were impervious just not enough people had them ;-) to warrant the time to make a program..