It's a question that plagues the successful and the aspiring: How much does a family need to net each year to lead a comfortable affluent life? We are not talking about great riches; there are millions of Americans who work hard to be able to afford the best for their families--and themselves--but who don't entertain notions of owning private jets, sprawling country estates or closets full of the latest fashions. Their goals are more grounded: a good education for their children, a nice house, a weekend place, the occasional trip, a night out once a week and a little money...