In fairness, I had a difficult time with codecs when I switched. I had some AVI files created with CamStudio and the Microsoft MPEG4v2 codec. I went through several Google searches and non-working installs before I found Perian.
For a lot of us, the Mac world is still foreign, and it's not as easy to differentiate between scams and legitimate programs in this new world. Add that to the fact that many switchers are sold on the idea that we don't need to think about this sort of stuff with a Mac (I *never* thought that, but anyway many do), and that's a recipe for disaster. And saying "it's a Trojan and not a Virus" is disingenuous, and dodges the point, since most non-technical folk consider all malicious programs to be a virus.
No matter how you slice it, this is another chink in the Apple armor. If they were smart, they'd find a way to push an update through Software Update to alert users when they're about to install known viruses, trojans, or whatever. Something that would let QT recognize known items on some kind of blacklist would be nice...
J