If I'd been asked, I would have said that income tax rates had stayed about the same over the last 30 years. Reagan lowered them, then raised them, then Clinton raised them and Bush lowered them, so on the whole not much change. Actually, when looking at historical statistics on the budget recently I saw that in 2010 personal income tax revenues amounted to 6.2% of the GNP, the lowest level since 1949. Of course, that's partly because of the recession--unemployed people don't have much income on which to pay taxes. But this I estimated a trend for the "full employment" --what income tax revenues would be if unemployment were 4%.
The figure indicates that income taxes have been dropping and are about where they were in the late 1950s. Of course, the numbers in the figure are from a statistical model, but if you want raw numbers, you can compare 2010 to 1982 and 1983, when unemployment was about the same but personal income tax revenues were 9.2 and 8.4 percent.