The wealthiest 10% pay 70% of the income taxes as is, the bottom 90% pay the other 30%.
http://www.ntu.org/main/page.php?PageID=6(the middle class pay a far higher % of the social security, fuel, sales, sin, consumption, etc. taxes than the wealthy and overall we tend to have a flat tax in america). Naturally, the GOP is only concerned with cutting taxes that the rich pay the majority of. You don't see them calling for a tax cut on social security, which is a regressive tax.
We collect about 1.2 trillion in federal income taxes, so I'm guessing that is about $150-200 billion in lost revenue.
I'm guessing cutting the corporate tax to 25% (corporations pay about 340 billion in income taxes) would eliminate $50-100 billion.
Anyone have any real numbers? I'm guessing we'd lose about $300 billion a year in revenue under the GOP plan of tax cuts for the wealthy which would be funded by cutting education, healthcare, science, energy and aid for the poor, disabled and elderly.