Being in the business, there are pros and cons. Had this discussion 1,000+ times.
Macs are nice machines. I love em. Good operating system, excellent for sound and video editing. They are also expensive and no choice in what hardware you get, not always bad. Software is more limited and slower to release. Still, if you can afford it, you will like it. Price drives many away.
PC's are more vunerable due to people who are click happy. One time, while doing a review of an anti-spyware program, I tried to get infected as a test (with no anti-malware tools running) and I could not no matter how hard I tried, and I saw some sick crap I have found that the majority of pc users click ok to anything. They typically are downloading illegal music, videos, porn or all of the above. If they are not, then a family member is. They also tend to fall for free screensavers and things that require you download a program to get a program or give up your email and more.
PC's are a huge target because Windows (98, Me, 2k, Vista, 03) are easily installed on the overwhelming majority of computers. When the security argument comes up, you simply need to read Apples and Microsofts patch release notes, they tend to look almost the same! Look at it this way, if you start a business, do you target 95% of the market, or 5% of the market? Theres no money to be made infecting Macs with malware. The most secure, stable computers are the ones not connected to the internet, used by one person, who never installs anything. A little knowledge goes a long way
