Kevin Drum reports this chart on tax progressivity, with the comment that "the US is more or less right on target."
This is wildly deceptive chartsmanship. Just because there is apparently a trend line here does NOT mean that all of the countries on that line have equal tax progressivity. That would only be the case if the line were at 45-degrees. But in fact, the tax share is increasing by 10 percentage points for every 4 points in income share. This means that, even for countries on the line, the farther right one goes (on the chart, not politically) the more progressive the tax system is, at least vis a vis the top 10% (Drum is probably right that you would get different results for the top 1%, but I think he is wrong to say that state tax systems are wildly regressive).
Here is the corrected chart. The further right of the red line, the more progressive, making the US system (again for the top-10% measure) the most progressive of those on the chart.
It is interesting to note that the original chart tells us one thing -- countries with wider income distributions have the most progressive tax systems. Which is an interesting and not necessarily expected outcome. Certainly it seems to refute much of the purpose for such systems in the first place.
Update: I am guess these are the data points on the chart, with analysis at the always terrific Carpe Diem