The Economist's Free Exchange blog refutes the common proposition claiming that income disparity has grown while middle-class income has not increased over decades. They quote Terry J Fitzgerald, senior economist at the Minneapolis Fed:
Rather than falling by 4 percent over the past 30 years, average hourly earnings have actually risen by 16 percent. Growth in the median hourly wage went from 12 percent to a more respectable 28 percent.
Large gains at the top end of the wage distribution might seem to be accompanied by flat wages at the bottom, but that is not the case. Wage gains at the lower end of the distribution held up fairly well. Wage growth rates at the 10th and 20th percentiles were only slightly below the median growth rates, increasing by 17 percent and 18 percent, respectively. While these data confirm that wage inequality increased since 1975, they also confirm that a broad swath of middle America experienced notable hourly wage gains.
While Russ Roberts says:
In 1970, according to the American Housing Survey (from HUD and the Department of Commerce ,then called the Annual Housing Survey, Table A-1, p. 32), 36% of the 67 million households in America had air conditioning, 11% had central air. This is the earliest data available from this survey.

In 2005, the most recent data from the same survey, (Table 2-4, p. 66) 82% of the 15 million households with income below the poverty line had air conditioning, 52% had central air.
I've long been saying that Americans don't know what "poor" is. The average poor person in the United States - the kind that's on social welfare - has a standard of living comparable to a middle-class person living in Slovenia today.

The difference is, the people in Slovenia feel smug about themselves. Most of them have never been to the States, yet a majority appears to believe the Delo ("Work", "Labor") newspaper as it tells them how "bad" income disparity in the United States is, and how "bad" the poor Americans have it.

This reminds me of an anecdote from Ion Mihai Pacepa's Red Horizons. Romanian dictator Nicolae Ceauşescu visited the U.K., and as part of his visit, he was taken to a department store, perhaps Harrods. He was impressed by all the goods available - but he found it impossible to believe that what he saw was the normal situation in a department store; it was impossible to find a store with shelves so full in Romania. He found it insulting that the authorities must have stuffed Harrods with goods they must have obtained on purpose from all over! How dare they think he would be misled like that!

Not to be outdone, when foreign dignitaries later visited Romania, he had all the paltry shops in Romania stripped of all the goods that could be found, and he had them all put into one store. Then a tour of that store was organized for the foreign dignitaries. See, in communist Romania, we have goods, too!