The brookings institute has published an article analyzing the effects of Romney's tax plan.
http://www.brookings.edu/research/papers/2012/08/01-tax-reform-brown-gale-looney
To put their findings in a single sentence,
http://www.brookings.edu/research/papers/2012/08/01-tax-reform-brown-gale-looney
To put their findings in a single sentence,
Our major conclusion is that a revenue-neutral individual income tax change that incorporates the features Governor Romney has proposed ... would provide large tax cuts to high-income households, and increase the tax burdens on middle- and/or lower-income taxpayers.