The argument behind this graph in The Wall Street Journal is that the middle class has most of the money and ties into a larger argument about who should be taxed what. There is after all a spike in the middle. Is that really the case though? Sound off in the comments.
(Cheat sheet: Jonathan Chait explains what's going on and Kevin Drum improves the graph to show more truth, although his graph can be improved, too. Grab the data here [Excel spreadsheet] from the IRS, and give it a go.)