Back when Avast was runnin a special for its Professional version (not the suite version), I got it for 3 years. Does its job, updates every day, doesn't hog the system when playing anything.
The free version of Avast even updates every 4 hours.
Panda Cloud Antivirus doesn't limit update intervals either, but it
depends on a steady Internet connection. As said, most of the other free stuff artificially limits you to 24 hours and makes you more vulnerable to 0-day exploits this way. That's why I think there's no real match to Avast, when it comes to freeware.
Locks are to keep honest people honest. Locks don't exactly stop those that have intent on breaking in. I live in a community with mostly honest people, no need for locks.
Reminds me of Michael Moore walking into Canadian people's houses.
And some minutes earlier, talking to a home security salesman. "An axe would do it."

But the net isn't that much of a community with mostly honest people.
ive had no virus protection on my computers for the past 6 or 8 years, havent had any problems at all. I use noscript, and adblock in conjunction with firefox.
If you need more then that for your home computer then your fucktarded.
NoScript is pretty paranoid by default. But it only protects you from shit that can happen while browsing. And it only works if you don't get accustomed to whitelisting sites anyway because your RapidShit download or your cute little kitty video wouldn't work otherwise. Same thing as accepting every Vista/Win7 UAC window out of reflex.
But if you are tricked into downloading a modified Firefox, µTorrent or even warez, NoScript won't help you a bit.
Relying on common sense is nice, but can you expect the same level of common sense from you parents and grandparents? And while you may be able to tell trustworthy from not, the crackers are of course trying to take this into account as well. Scams are getting better and better.
AV programs alone don't solve the problem. To be somewhat secure from rogue applications, you'd need to prevent non-signed programs from running, yet continuously apply patches to fix security holes. You couldn't run old games in administrator mode to have them work under newer versions of Windows. Etc.
Once they get real, people will have to choose to live with the restrictions or act like a fucktard to at least have a computer that just works™. Many users will choose the fucktard option, even in business scenarios. (or from my experience, especially in non-technical business scenarios

)
So it isn't a bad idea to get an AV scanner and be happy if it never detects anything, to check the integrity of your executables and libraries (have they been modified without your knowledge), to use recent and stable software release (most Linux distros are good at updating, check out
Secunia PSI for Windows boxes) or to make sure you aren't exposing any unwanted service to others (a NAT router should do in private scenarios). Add you common sense, and you have a somewhat decent security package.
Also, if your box has been infected, you don't have to worry about your porn that much, but more of the botnet it might be part of.