The only thing which has kept Mac OS X relatively safe up until now is the fact that the market share is significantly lower than that of Microsoft Windows or the more common UNIX platforms. If this situation was to change, in my opinion, things could be a lot worse on Mac OS X than they currently are on other operating systems.
In my experience-- which is also the experience of some of my peers- Apple has been very slow to respond to reported security vulnerabilities. It expects security researchers to wait indefinitely to release the vulnerabilities and offers no incentive for them to do so.
I would hope that most people would be aware that there is nothing protecting them from file based infection on their system. However it would seem most people think they have an invisible bubble protecting them from harm.