As America sees record numbers of new millionaires (see posts on Justus for All) the poverty rate also continues to increase. America has the highest poverty rate of any industrialized nation, and it continues to slowly climb each year. According to the US Census, the poverty rate was 11.7% in 2001, and up to 12.7% by 2004 (the latest figures). This shows wealth being concentrated in the hands of a smaller elite. When the upper class and the impoverished class both continue to grow, the middle class necessarily decreases. This effect is more pronounced in the rest of the world. Between 1989 and 1998, the number of people living in Latin America on two dollars a day or less grew from 33.7% to 35.8%. This number is even worse taking into consideration that those are real dollars, not inflation adjusted.
UPDATE: As an example I lifted this chart from the IMF webpage. It shows growth in per capita income for all people in the world, but more striking is the growing difference in the income of the upper quartile and lower quartile. Not shown is a chart of inflation to compare this against. Also, it is noted on the IMF website that although this chart gives the impression that all per capita incomes have increased, some poor countries have actually seen an inflation adjusted decrease in per capita income. Others have seen a real decrease in actual dollars. I am still looking for a chart that breaks down exactly how much wealth is controlled by the upper quartile versus the other three.