If you want to spend the money, go for it. But it REALLY IS NOT NECESSARY if you don't surf to stupid places. Heck, even if you do, OSX will be fine whereas the other major OS would be getting attacked.
Consider this:
In order for a virus or other malware to impact your OSX machine, YOU have to let it get installed. Generally speaking, the malware out there in the wild written for Windows needs to be deposited in certain directories and execute certain functions. You are running OSX - not Windows. This means those directories are in different places which means the executable code that places the bad files cannot find the directory and cannot be installed. As the other poster said, there are currently no OSX viruses in the wild. Yes, that can change - but if you keep up with the updates from Apple, those exploits get resolved (by using proof of concept work) before they hit the wild... A portion of this is the same explanation as to why you cannot install and use applications (like Word or Excel or PowerPoint or whatever) written for Windows on a Mac running OSX... The file structure is different. The Operating System is different (OSX is a GUI on top of a Unix variant).
Does this make sense to you?
Asking your question again is not going to get you a different response.
I can't seem to get a straight answer. I realize that macs can't get viruses, but what about spyware programs? On my pc, every time I ran the anti-spy it would find at least twenty things. Will this happen with my mac? Would downloading yahoo anti-spy be a waste of time? Or, is there a better; free anti-spy program out there? I notice that Norton (and I think McAffee) both make anti-virus/ anti-spy programs for macs that cost money; so if these were unnecessary, why do people buy them? I realize the answer is probably just "because they are stupid", but perhaps there another reason?
Thanks to anyone who can help answer whether or not I need an anti-spy program for my new macbook pro.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic