My overall takeaways from the book were:
1. Class is correlated with income, but not identical.
2. Class is so ingrained in so many areas of our lives that it's almost impossible to change. You might as well just be comfortable with the class level you grew up in, because you'll probably always be there.
3. A big reason for #2: caring about your class in the first place is middle class. The more you care about where you fall in the class hierarchy, the more middle and upper-middle class you are. Lower class folks don't really care (and may even take a certain amount of "pride" in being lower / working class), and upper class people have nothing to prove to anyone.
But the book goes into excruciating detail about the way people dress, speak, decorate their homes, what jobs they have, cars they drive, etc, etc.