It'll be interesting to see if they will keep doing this as more and more malware (including viruses) gets written for Mac OS X...
Viruses (using the actual definition of a virus) I still believe are very unlikely to become an issue on the Mac.
Social engineering (i.e. getting users to install malware) will be the biggest issue facing the platform.
It appears Apple is taking responsibility and exercising due diligence as platform vendor.
That said and whilst you should never be blasé about security: Mac OS X has never been the platform where arbitrary code coming from the internet gets executed easily. It can still happen and people will no doubt miss the point and reply citing examples of security conferences etc., but in the real world exploits are rare.
If malicious code does run key aspects of the system are sand boxed (since leopard).
Almost any code coming from the internet is quarantined until the explicitly confirms they wish to run it (again, since Leopard).
And then Snow Leopard has the anti malware scanner and the beginnings of a ASLR mechanism (albeit not the best).
And many if not all Apple updates are now being digitally signed. As is anything you get from the Mac App Store.
I don't have Lion, but I imagine it has added some more protection.
I find some of the media analysis laughably naïve that Apple has somehow reached the level Microsoft reached in 2001/2002 with Windows XP and it is all downhill from here.
Microsoft's learnt a lot since then, the whole industry has learnt a lot and Apple hasn't been blind to the lessons learnt.
Apple are building up the walls slowly and steadily in response to the threat and anyone paying the slightest bit of attention would have noticed.
That is why I think the “floodgates are going to open” doomsday merchants are very wrong.
