In my experience (when properly configured) both operating systems are secure and reliable. Companies and organizations need to do end user education about best practices (e.g. what attachments to open, web sites to stay away from, don't click on website ads that look like system dialogs).

Are Macs more secure than PCs, or not? Either way, the answer always drives Windows users nuts.

The real question about Mac security

With Windows (and I'm speaking of Windows XP...Vista should not even be considered until they make a number of improvements) the bigger problem is rot. Anyone who has used Window XP for any length of time knows that is slows down considerably (and becomes less stable) the longer you use it. Eventually the only way to regain the speed and robustness is to reinstall the operating system (and because of the way DLL are spread throughout the system...many of your applications). I'm not sure if rot has been addressed or if Microsoft is hoping that faster hardware will minimize this "feature."