"Firewalls and anti-virus software are good things to have - but so far, Mac users have survived without them."
Uh - since 10.3 dosen't OSX have a built-in firewall ?
I suppose the Mac design folks have decided it's a good idea to have one.
It does, but it's turned off by default. It can be activated in the System Preferences - Sharing control panel.
More importantly, Mac OS X doesn't have any unnecessary open ports or services running.