Class is defined by 4 things: Wealth (How much land/stocks/stuff you have. The top 1% of this country owns 80% of US wealth, leaving probably 15 - 20%to the middle class.), Income (Salary/wage of generally $60,000 - 150,000 or so, possibly more per year), Education (Generally middle class people have at least some college education), and Prestige (How respectable your job is, so that is why a plumber can be paid more than a IT person, but is considered working class).
Most people think the middle class is the class they are in. They think this because they know someone who has more money than they do, and someone who has less. Really, the middle class only makes up about 30% of the US population. A MUCH larger silent working class exists. The poverty line is a false indicator of middle class, as it is unsustainable and really the definition of "emergency poverty." Another words, financially, nutritionally, health-wise, families cannot make it when consistently within 200% of the poverty line without help.
The middle class is actually also a bit of a myth created by school and the media. It is seen as the ideal when in fact, in truth, it is out of the generosity of the working class (basically being underpaid to do all the grunt work that someone has to do) that keep the gears of this country well-oiled.
Sorry to break your bubble!
However, one must ask oneself how to define class. Perhaps financially or culturally? It has been asserted that you do not need to be restricted to relative material wealth in order to be middle-class. Rather, you can still have middle-class values. If this is true, then one can assume that there is still working-class values thus the statement that there ceased to be a working-class in the 1970's is false. Furthermore, that even if they have two cars and take several holidays a year they are still distinctly working-class. Often it has been asserted that money does not buy you class or status. Certain Neo-Marxists now assert that the working-class are transforming into a "Service Class" for the 'infomation workers'. For example, service class's may work in Supermarkets on checkouts, providing a service for people who are employed in the IT industry.
A stereotypical middle-class family might consist of two parents, married, living in detached house with two cars and a well maintained garden. Their children, both at university. They enjoy dinner parties and have many cook books and dabble in Red Wine probably far to often. This is merely a stereotype though, you'd probably be suprised how many have fairly bizarre patterns of behavior such as Swining or Heroin addiction.
See the films Blue Velvet or American Beauty for accounts of the American middle-class. Alternatively George Orwell wrote exstensively on the class system in Britain in novels such as "Down and Out in London and Paris" and "Road to Wigan Peer".
"We're having a dinner party tonight, don't bloody forget the Red Wine again Paul!"
"George, can we jock the gimp suits tonight and get cracking with the cocaine whilst the kids are away?"
Thinking: '...that's a nice jeep'