Bloomberg reports on how Mitt Romney used a type of generation-skipping trust known as "I Dig It" to dodge gift and estate taxes: 

Here’s how they work: the person setting up the trust, like Romney, contributes assets such as an interest in a fund or shares in a company. If he makes that contribution before those assets appreciate -- particularly when they are privately held and difficult to value -- he can claim the gift tax obligation is low or non-existent since the declared value is low or zero.

 

If the trust generates any income -- such as by selling stock -- the eventual tax bill is the responsibility of Romney, not the trust. By paying the capital gains tax, which was 20 percent in the late 1990s and is now 15 percent, he can avoid depleting the funds in the trust -- in essence making an additional donation that’s free of gift taxes.

Romney would eliminate the estate tax; his tax policy paper says the tax "creates a series of perverse incentives that encourages the most complicated and convoluted tax-avoidance schemes at tremendous cost to all involved."