I'm always vigilant against this spammers, malware, and the like. In fact anyone's computers that I'm near normally gets a quick glance to make sure their AV is running any up to date. I tend to stay off of dogey sites, so I don't worry much and I have MS Security Essentials running for AV and Spyware. I manually do full system scans weekly unfortunately Malware Byes is 32 bit only so it won't run on my new Windows 7 install but I'm looking a decent replacement.
One of my biggest beefs with security software is
most of them when to run as a live resident scanner, AV is enough for me. It just bogs down the system live scanning all file system changes
It's great that Microsoft put out MS Security Essentials it's consistently received rave reviews and is light on system resources. I used Avast for quite a while but it was getting a little bloated lately. The first thing I do on a computer that someone says is slow is uninstall Norton/McAfee and install MSE. It's free and light on resources.
For my part, I think people should take some time to learn about their computer. You wouldn't drive a car without knowing the basics a little knowledge goes a long way to thwart viruses, bot nets, and social engineering.