I don't install software I don't need. About 90% of my friends/associates use Macs, and I've never heard of one getting a virus. Sure there are vulnerabilities with any system, but rarely do attackers target Macs (like you said, it's a numbers game). If there ever is a virus problem, I'd use...
Yeah nobody had mentioned it. Had to throw it out there! Ubuntu is cool. Has come a long way for sure. I had a xubuntu file server for years. It was one of the old DP Quicksilvers with a RAID 1 array. Loved that thing, but eventually moved to remote backup, and mostly online document sharing...
I stopped using IE in 2003. Went to Firefox (then called Phoenix). Used it till 2009. I use Chrome now. So fast and simple. Has only one 'bar' for searching and URLs. Opens so fast. Did I mention it's fast? Tab behavior is nicer than FF too. Oh it's also quick.
I only use FF for development now.