FWIW, the "marriage penalty" doesn't kick in for savers until you are quite high income. For the 10 & 15 percent brackets, the income range is exactly twice as high for married couples. In the 25% bracket, you don't max out the bracket until $148,850 as a married couple as opposed to $89,350 for individuals, but keep in mind that it's extremely rare to have identical income earners. Usually it is a 2:1 or at least 3:2 ratio, so filing jointly is still helpful.
At any rate, let's answer the question: "Where does the marriage penalty truly kick in for people who save a lot?"
To answer that, I'd start at the top of the 25% bracket of $148,850 and then add in everything that would normally not count as income. Standard deduction and personal exemptions add up to $20,300. 401k for 2014 was $17,500 so that's another $35,000. Suppose you have $5000 of employer covered healthcare benefits. That's a whopping $60,300 of income that is shielded from federal taxation, which means you can gross about $209,150 as a married couple and still slide in at the top of the 25% bracket.
IMHO, somewhere in the neighborhood of $210k/year of ordinary income is a crapload of money, and I'm not even counting child tax credits, EV car tax deductions, or any of many other thousands of dollars of deductions or credits a high wealth family typically is eligible for. To cry about a marriage penalty when you're making over $210k/year falls under the category of being a baby about it. You're at 4X the median household income for Americans at that point. Nothing to get complainypants about.
