I've been a Mac user since they first came out (1984) and my LAN at home has four of them. Actually, I'm the only one using a PC and that's so I can be compatible with work (I'm an IT director and deal with Windows issues all day long). My wife and kids are doing just fine with their Macs.
My laptop has to be "cleaned" weekly - virus check, AdAware, AntiSpyware, disk defrag. And it still runs slower and slower all the time. Solution - buy a new one and start over. That's what M$ wants you to do. I constantly get calls from non-tech friends who need help fixing their Windows machines. I would go maintenance crazy if my wife and kids had Windows PCs.
I quit worrying about viruses on the Macs - they don't get them. Sure, they could, but I'm not going to worry about it. The new Macs with the Intel chips will change the playing field a lot IMHO, but it's the underlying UNIX operating system that makes these Macs so awesome. UNIX is a much better designed OS than Windows. Why do you think supercomputers and most Internet servers run UNIX? Windows needs a complete rewrite to get away from the constant patching.
Take a look at Keyboard Mag and you'll see that there's an abundance of Macs in the recording field. Why? Ask the recording artists and I'll bet they say they are easier to use.
I'm telling people these days that if they plan to mostly surf the net, send e-mail, store/edit photos and music, burn CDs and DVDs of music and video, MIDI - get a Mac.
Also, much of what anyone does these days is fast becoming web-based so it often doesn't matter what platform you use.
Sure, there are programs available only for Windows. Some of the tools that deal with arranger keyboards come to mind. If that forces you to remain a Windows user, go for it and learn to live with the maintenance issues. If you can swing it, keep a Windows laptop for use with your arranger tools and use a Mac for the rest of it.