Why I use a Mac, anno 2006 3715
Hehe. That's not the computer, that's the OS. The only reason it's more secure is that hardly anyone uses it. It has been proven that OS X(Unix) can get viruses too and you don't have to give it permission to copy itself to the Mac's memory. So if you're main concern is security, there are many tools to help you whatever OS you have.
Why I use a Mac, anno 2006 3716
Since this is c.s.mac.advocacy, we clearly cannot let all this pro-mac stuff stand unanswered! :D Those "security updates" are not for show; Apple really does have vulnerabilties, and if you don't patch...
This is true for any computer, you take precautions and you can use your computer with very little worry. However no matter what the security on OS X or what, viruses, trojans and worms can still get through.
You could do that on a PC with Unix in stalled or you can have OS X installed if you know how to do that with a PC. Actually this argument is really invalid because the Mac is now a PC clone and it can run Windows and OS X. Over the shelf PCs can do the same thing.
This is not a good argument since a PC can be run for months and years without a crash. I've seen a Linux PC run for years without a crash. I've seen a Windows XP run for months at a time and no crashes. But the Windows XP system only went down for an upgrade and it got more use.
What war? Haven't you heard? Macs are now actually PCs with EFI instead of a BIOS that shows up on most PCs. The war is over.