I've followed the flat tax debate over the years dating back to Rep. Armey's failed proposal back in the 90's to it's inclusion as Steve Forbe's platform centerpiece in 2 presidential campaigns.
The concept to simplify an overburdening tax system is embraced across party lines, but there is no clear cut agreement on the means of implementation. A flat tax proposal has to address the individual tax system, business and corporations, and Social Security. Income, revenue, and expense would have to be redefined under new terms. We don't have just simple income in the U.S.; we have Adjusted Gross Income. Every line item entry that adjusts income would have to be reevaluated.
It's success in Eastern Europe further champions its legitimacy as a viable taxation system. The long term benefits are unquestioned. But the show-stoppers are likely the cost to overhaul and implement a new system and the possible ensuing chaos during the transition. It won't happen if it destabilizes the economy.
Brownback and Giuliani are flat-tax proponents, with Giuliani only recently hoisting the flat tax flag with Steve Forbes now running his campaign. I've actually downloaded many of their position papers and speeches, along with many of the other candidates, but I haven't had a chance to read them all.
Here's Brownback's:
http://www.realclearpolitics.com/art...lat_tax_1.html
And Giuliani's sudden backtrack on the flat tax issue:
http://www.nytimes.com/2007/03/29/us...prod=permalink
In regards to fl8ntive's mention of the FairTax concept,

, Boortz's book is a must read. Going to a fixed rate sales tax has to be considered (and debated in this election). But the poll was regarding flat tax, so maybe a discussion of the FairTax concept should be held in another thread.