I did not.
There was an article somewhere that I can't find now about how they do it. It was more of an example than anything, but it was something like this:
Zuckerberg would pledge his FB stock against loans he took. Since it is a loan, it is tax free. Say he takes $20M/yr in loans. He is 37, so over the next 50 years, that is $1B in loans. Plus another $1.5BM or so in interest. So he now owes $2.5B. He is worth $132B. So he dies and his estate must settle his debts. Since he is now dead, his estate can sell his FB stock at current value to pay off his debt and still not incur any taxes.
To kind of give an idea of the difference between 1M and 1B, here is an example most people can relate to. One million seconds is just over 11.5 days. One billion seconds is over 31.7 years.
And it is all 100% legal.