**facepalm***
see folks, this is why they say the #1 security is the user, when that fails, any subsequent measures, lol, manual scan*ahem..will remain fruitless. This kind of mentality is why botnets are so prevalent.
So your saying that my monthly boot from a liveCD and running of antivirus from there would never detect the same things having memory resident antivirus would detect? Bullshit.
The fact that no virus scanner has ever detected a single virus on my computer, and the same process has found viruses on my parents computers (who do run antivirus all the time because I know they need that kind of protection) vindicates me.
I am security conscious, even as a full time mac user I still keep up to date on all exploits. I don't run flash, I block all ads before they enter my network, I don't use acrobat reader (I stick with pdf readers with a proven track record), I never run as administrator (even on windows). On windows I even took the extra step of running my browser in a sandbox. I scan all downloads for viruses.
I'll just come out and say it, my security practices are better then 9/10 people you will find on the internet and that 10th guy probably works for a security firm.
Memory resident antivirus are for people who are either unable to control their own security, or just want that extra layer of protection. They are not bad, but they are not required. The same with running a firewall on your PC. My network has a hardware firewall and it's just my wife and myself (and she's just as good as I am). We have a separate guest network for anyone else who needs access. We leave the OS built in firewall turned on because it's there, but going out and buying/downloading another firewall product is silly.
No measure of security can protect you from yourself. Don't run as admin, don't download from untrusted sources, and use nonscript/flashblock or it's like on your browser (or sandbox your browser). The antivirus is just an double check.