Herman Cain's 9-9-9 plan has attracted lots of attention. Paul Krugman cites a Tax Policy Center study that shows the plan penalizes middle and lower income households.
The main idea is that there are people who will pay more taxes and those who will pay less under every income group. The impact of the tax policy depends on the mix between those paying more and those paying less.
The data table is far too cumbersome to bring out the message. Here is a visualization: