Who wants to be in the Middle Class? Class lines and economic inequality

While reading a rant on a site by someone who considered herself "lower middle class" and therefore unable to afford certain things in life, I began to ponder where the class lines are really drawn. She quoted her earnings, and that didn't scream lower middle class. To me it was in the middle, maybe even a little better.

So I went on a quest to find out how we define those classes. I came across one estimate from 2005, with the source cited as the U.S. Census Bureau. Take a look at these numbers:

I got to looking around the Census Bureau's site, and was interested to find all sorts of statistics and narratives on "income inequality." That got me thinking even more.