Call me
Call me when something is found that can compromise root on the Mac without user intervention. Then the Gates towelboys will start to have a valid point.
I'd hardly consider social engineering to be a platform issue, more of a clueless user issue. Unfortunately, those types of users exist on every computing platform that has ever existed. Simple fix: I've disabled root/admin access to users on machines I administer. Easy to do on Unix/Linux/MacOSX. Much harder on MS Windows.
So my users have received several trojans, but it has no effect because Unix/Linux/MacOSX systems have adequate (but not great) security. The very few remaining MS Windows users have, unfortunately, managed to corrupt their systems even with all the extra software and hardware that has been deployed to protect users from their own idiocy. Frankly, they're more work than it's worth, and I've given them notice that their support for MS Windows terminates at the end of the year.
In summary, in Unix/Linux/Mac you can avoid a lot of user problems by not giving the user root access. In Windows... you can't, because at its core it's still a single-user system and applications constantly require root access to operate successfully. So applications have to all run in root mode, with horrible consequences.
All commercial operating systems made to date have serious flaws, mainly due to flawed design processes that are driven more by marketing than by science. MS Windows, unfortunately, has more flaws than most. No amount of marketing can change that fact. Just because it's popular doesn't mean it's any good.