What are the arguments for and against using the macintosh operating system?

I use a PC because it is cheaper, from my understandings a Mac is expensive but will out last a PC with minimal upgrades, I was in JB Hi Fi the other day and Norton has an Anti Virus program for Mac's , so they are no immune as one would believe? I have spoken to people that have used a PC and gone to a mac, and say they will never go back? I have seen then on display with all the apps open and they are still fast,were a PC would be starting to slow or lag? From other observations, you could by a 2 year old mac and the software etc would be still on a par with the latest where a PC may have gone through a SP and numerous security updates etc? Expensive but in the long run worth it.