I've heard people talking about flat income taxes in Switzerland but all of my personal research on the internet points out that the country has progressive tax rates, even for corporations. Eg: http://www.estv.admin.ch/data/sd/e/system/fremd/3.pdf
The rates at which the Federal Direct Tax is levied are progressive; a zero rate on the first income bracket is followed by nine brackets with progressive rates, reaching a maximum of 13,2% and then declining to 11,5%. Brackets as well as deductions are subject to formal indexation entering into force when the inflation rate has risen by at least 7,0% since the last adjustment. http://www.henleyglobal.com/swisstax1.htm
Due to the interrelation of Federal, Cantonal and Communal taxes, the complex tax rate mechanism as well as the different deductions available, it is extremely difficult to give a precise indication of tax rates applicable in Switzerland. Federal income tax rates are progressive. They range from 0% to 11.5 %. However, Cantonal and Communal tax rates vary depending on the Canton and the Community involved. On average, they are generally twice as high as Federal rates, so the total final combined tax rate may exceed 30% for high income earners. Effective tax brackets across different cantons, the rates are all progressive: http://www.estv.admin.ch/data/sd/e/system/fremd/5.pdf
Also spouses could aggregate their income for tax purposes (ie. income splitting), not a very good example of tax neutrality. Last but not least, major tax reforms should be required if we'd like to adopt flat income taxes. Economics 101, thou should not distort relative prices. Perhaps we could start by making capital gains fully taxable.