Harvard Economist Barro is opposed to any marginal tax rate hikes:
http://www.aei.org/article/102520
A study by Moody's finds that the rich are more influenced by business cycle developments rather than tax rate changes
http://www.businessweek.com/news/2010-09-14/america-s-wealthy-save-tax-cuts-rather-than-spend-moody-s-says.html