A surprisingly well balanced review of the current state of flat taxes is to be found in last week's Economist. It concludes:

On balance, it would seem that the flat-tax revolution is more likely than not to slow, and even reverse eventually, as the income gap between western and east-central Europe narrows.

In other words, the phenomena is a simple one that has been required to assist the transition from disorder to order, but has nothing to offer developed economies. That may well be true.