Yes and no... We've seen a couple of minor exploits in iOS (ie - Jailbreakme.com) where a site gained root level access without Apple's permission in an arena supposedly completely controlled by Apple. There is no such thing as a perfectly secure OS. Apple does a better job than Windows in some respects, but Win 7 is remarkably better in that regard. Also, MS now provides free AV protection as well, cleaning up their own mess, so to speak...
I know I'll get blasted for saying it, but Windows and Macs are mostly being targeted the same way now (Windows more so, but there are still more Windows boxes out there). It's all about tricking the user, not breaking the system. Both OS's are reasonably rock solid when it comes to system attacks... Windows patches more often, but really, they haven't had anything in the way of major attacks in a great while... Conficker happened when? And it was kind of a dud in a lot of ways... Pretty much, now the user has to allow stuff to happen outside of their profile.