>I'm surprised to hear that some Jews don't observe Yom Kippur.

Just as there are Christians who consider themselves Christian but never go to church except Christmas, there are Jews who never go to synagogue except on the "High Holidays" (Rosh Hashanna and Yom Kippur).

Just as there are Christians who never go to church there are Jews who never go to synagogue at all. They don't observe any of the laws or rituals "required" by the religion. For many years I was one of them (eating a ham and cheese sandwich during Passover, for example). But they (we) still identify ourselves as Jews with a strong attachment to the cultural and ethnic aspects of being Jewish. And, except for the ultra-orthodox, they are recognized as Jews by those who are more "observant."

>While in college I was caddymaster at an all Jewish golf club on Long Island.
>The members were widely divergent in their religious observance the rest of the year but absolutely no one played golf on Yom Kippur.

I suspect that is more of a matter of social pressure than religious observance. There would be a social stigma attached to playing golf on Yom Kippur at that club. My strong expectation is that they were playing somewhere else. Or perhaps even at work (yes, there are Jews who go to work on Yom Kippur).