OK, this guy will give you his version of middle class defintion and it’s history from 1979 to 2007. My idea of middle class (according to his defintion) would include upper working class as well; again it’s all about income, mindset and lifestyle.
Here’s some historical perspective from an article back in 2003. See if it sounds familiar to you.
For more recent history (up to 2006) on middle class wages and earning power follow this link.