If you use Linux with software it crashes many times, my Vista never crashed, I use Antivir and Spybot and I never had virus problem. I think that if Windows is the most popular OS it's not a case! I really want someone can make change my mind!
It must be a matter of personal experience and which distro you use.
In my experience openSUSE is rock solid. As to Vista, until recently it kept crashing on me beyond recovery after a Windows Update or even installing a simple app like Firefox. Not to mention the lack of drivers or the terrible compatibility with programs I owned.
As to OS X I find it also rock solid. However these days I use openSUSE more often because I find it more flexible for my needs.
Why is Windows the most popular OS? Because they came before the others with a cheap OS for beige hardware. These days it is preinstalled on most PCs. However even Microsoft is beginning to realize that Vista is a potential failure (by allowing everybody to downgrade and by extending XP availability).