A 90% marginal rate on personal earnings is a bit ridiculous. In order to get to that point at a million dollars, you'd most likely have taken away $750,000 already.
Secondly, have you heard of the one-dollar CEOs? A lot of tech company heads, because they have so much secondary income through shares of the company, can avoid paying that 90% personal income tax by making their salary just one dollar.
I think what we need isn't so much a higher income tax rate (especially on wages), but bringing the tax rate up on investment earnings over certain thresholds. A capital gains tax of only 15% when the income tax for the same amount is 35% is kinda just asking for people to redirect all their income in that direction.